From Higginbotham's (2019) Midnight in Chernobyl, the Untold Story of the World's Greatest Disaster (emphasis mine)
The recollections of others present at the time would be quite different. According to Toptunov, Dyatlov not only witnessed the power fall but also—enraged—told him to withdraw more control rods from the reactor to increase power. Toptunov knew that to do so could certainly increase reactivity but would also leave the core in a dangerously unmanageable state. So Toptunov refused to obey Dyatlov’s command.
“I’m not going to raise the power!” he said.
But now Dyatlov threatened the young operator: if he didn’t follow orders, the deputy chief engineer would simply find another operator who would. The head of the previous shift, Yuri Tregub—who had stayed behind to watch the test—was well qualified to operate the board and right there at his elbow. And Toptunov knew that such insubordination could mean that his career at one of the most prestigious facilities in the Soviet nuclear industry—and his comfortable life in Pripyat—would be over as soon as it had started.
Meanwhile, the reactor continued to fill with poisonous xenon 135, falling deeper and more inextricably into the well of negative reactivity. Finally, six long minutes after the fall in power had begun, Toptunov, terrified of losing his job, gave in to Dyatlov’s demands. The deputy chief engineer withdrew from the console, mopping sweat from his brow, and returned to his position in the center of the room.
In his end notes Higginbotham writes that he is quoting from Medvedev's (1991) The Truth About Chernobyl. Medvedev was a Deputy Chief Engineer at Chernobyl and conducting extensive first hand interviews. Higginbotham writes "Medvedev writes that Toptunov would recount his thoughts [less than 24 hours later] while in the medieval center in Pripyat. He also claims "this view is expanded on by Shcherbak's interviews with Kazachkov and Uskov in Chernobyl 366-69 and 370-74" but I don't have access to those.
In The Truth About Chernobyl Medvedev writes (p54-55)
The situation in the room housing the main control panel of No. 4 reactor unit was one of high drama. With uncharacteristic energy Dyatlov ran around the operators' control panels, spewing forth a torrent of curses and foul language. His normally hoarse, quiet voice now took on an angry, steely tone. "You goddam idiots, you haven't a clue! You've screwed everything up, you boobs! You're ruining the experiment! I can't believe what a bunch of assholes you are!"
His rage was understandable. The reactor was being poisoned by decay products. There were two options: increasing the power immediately, or waiting twenty-four hours for the poisons to dissipate. He should have waited. Dyatlov, you overlooked the fact that the core was becoming poisoned faster than you had thought. Stop now and, and mankind might be spared the Chernobyl disaster!
But he was unwilling to stop. Still cursing, he dashed frantically around the control room, thus wasting valuable minutes. He ordered an immediate increase in the power of the reactor. Dyatlov continued to rant and rave.
Therefore Toptunov made the only correct decision.
"I'm not going to raise the power!" he said firmly. Akimov supported him. Both men explained their apprehensions to Dyatlov.
"You lying idiot!" Dyatlov turned on Toptunov, shouting. "If it falls from 80%, the rules allow you to increase power after twenty-four hours, but you fell from 50%! The rules don't say you can't do that. If you don't increase the power, Tregub will."
This was psychological warfare (Yuri Tregub was the shift foreman who had been relieved by Akimov and was still present, intending to witness the tests). Admittedly there was no way of knowing whether he would have agreed to increase the power level. Dyatlov, however, had guessed right: Toptunov, intimidated by his boss's shouting, acted against his own professional instinct. He was an inexperienced man, of course, of only twenty-six years old. He must have been calculating the odds: "The operational reactivity reserve is twenty-eight rods. In order to offset the poisoning, we're going to have to remove five to seven rods from the reserve group. I might cause a power surge, but if I don't do what I'm told, I'll be fired." (These remarks were made by Toptunov in the Pripyat medical center before he was sent to Moscow).
Serhii Plokhy in Chernobyl, The History of A Nuclear Tragedy (2018) quotes Razim Davaletbaev, deputy chief of the turbine unit who was in the control room on the right (from a Russian text published in 1995) regarding Dyatlov's conduct earlier on the night....
Immediately upon the start of the shift, Diatlov began demanding that the program continue to be carried out. When Akimov sat down to study the program, Diatlov began reproaching him for working too slowly and failing to pay attention to the complexity of the situation that had arisen in the unit. Diatlov shouted at Akimov to get up and started insisting that he hurry up.
And quotes Trehub/Tregub on Dyatlov's managerial style in general (from Shcherbak's *(*1991) Chernobyl again:
“He stopped off at Unit 3 on his way and evidently found something wrong with regard to discipline. He dressed them down,” remembered Trehub. That was typical of Diatlov. “He punished personnel severely for mistakes and disobedience, bellowing at them and fraying nerves,” recalled another colleague
As Rumbuck says in this thread we'll never actually know for sure, because it appears that the regime's response was to lay the blame on this one man rather than structural problems with the plant resign or the nuclear programme as a whole. But it would seem there is enough material floating around in the historical record to warrant saying he's was a belligerent guy not at all above bullying subordinates and it seems plausible, stressed as he was about getting the test done, that he would have threatened Toptunov with replacing him if he didn't do as ordered. Worth noting, in passing, that Toptunov actually was replaced as the events continued:
With Akimov’s assistance, Toptunov switched off the automatic system controlling the rods and began withdrawing them manually to breathe life back into the dying reactor. Trehub was also there to help. “Why are you withdrawing [the control rods] inconsistently? This is where you should be withdrawing,” he told Toptunov, who was initially taking them out of some sectors of the reactor but not from others. Trehub eventually replaced Toptunov at his work station and brought the power level up to keep the reactor going.
(from Plokhy (2018), quoting Tregub's remarks in interview with Shcherbak) (my emphasis).