So the passage your article cites as evidence for this story is Pliny Natural History 21.9. That reads:

​

At the time when preparations were making for the battle that was eventually fought at Actium, Antonius held the queen in such extreme distrust as to be in dread of her very attentions even, and would not so much as touch his food, unless another person had tasted it first. Upon this, the queen, it is said, wishing to amuse herself with his fears, had the extremities of the flowers in a chaplet dipped in poison, and then placed it upon her head. After a time, as the hilarity increased apace, she challenged Antonius to swallow the chaplets, mixed up with their drink. Who, under such circumstances as these, could have apprehended treachery? Accordingly, the leaves were stripped from off the chaplet, and thrown into the cup. Just as Antonius was on the very point of drinking, she arrested his arm with her hand.—"Behold, Marcus Antonius," said she, "the woman against whom you are so careful to take these new precautions of yours in employing your tasters! And would then, if I could exist without you, either means or opportunity of effecting my purpose be wanting to me?" Saying this, she ordered a man to be brought from prison, and made him drink off the potion; he did so, and fell dead upon the spot.

There are some reasons to doubt the historicity of this episode.

1. As the nineteenth-century translator of the passage observes, the Romans had no poisons capable of killing instantly. So the story as written cannot be factually true. This is worrisome.
2. Pliny the Elder was a compiler. His Natural History is full of facts and anecdotes about animals, minerals, and plants that he culled from a vast range of sources. The context of the above passage is a discussion of floral crowns and the possible health dangers they pose. In other words, Pliny is not writing a history of Antony and Cleopatra, simply re-telling an interesting anecdote that tangentially relates to his main subject. We do not, as far as I know, possess the source from which Pliny took the tale. So the story exists in isolation with no larger narrative whose accuracy we might test, and it is related to us by an author who had no particular reason to question its truthfulness closely. This is worrisome.
3. The story portrays Antony as a hostage or tool of Cleopatra. This way of thinking about Actium and the last civil war goes straight back to Octavian. Octavian framed his war with Antony as a war with Egypt, because it was easier to think of the Romans fighting a foreign foe than it was to admit they were in yet another civil war. Thus, it was Cleopatra and her courtiers who were the true threat to Rome. Antony was a pawn. According to Plutarch, Octavian argued that Antony "was drugged and not master of himself" (Plut. Ant. 60.1). Indeed, in the Triple Triumph of 29 BC, Augustus celebrated his victory over Cleopatra at Actium, and his conquest of Egypt, not his victory over fellow Romans. When the poet Horace wrote an ode celebrating the victory, he wrote "Now there must be drinking/....Before this, it was a sin to draw out wine/ from ancestral wine cellars, while the/ queen of demented people was preparing/ the destruction and fall from power for the Capitoline" (Odes 37.1). Once more, the civil was considered a war against Cleopatra. Finally, in the account of Plutarch, Antony is portrayed as completely undone by his love for Cleopatra. Because of her wiles, he decides to stake everything on a naval battle, despite having the inferior navy and a strong land army (Ant. 62.1). The point is that there was a strong tradition in antiquity that Antony was not his own master on the eve of Actium. The fact that the reasons why he was incapacitated (drugged, smitten, afraid) differ from telling to telling does not inspire confidence. So the story easily fits into a set of widespread (and probably false) narratives about Antony. This is worrisome.
4. Cleopatra is strongly associated with both poisoning and partying. The poisoning association stems, of course, from the story about her suicide by asp. Plutarch has her testing poisons on prisoners to find the quickest, a story that echoes the poisoned chaplet anecdote (Ant. 71.4). The fact that he knows at least two separate accounts of how Cleopatra got the asp to bite her (and a third account that said she just used poison hidden in a hollow comb) shows how such stories proliferated (Ant 86.1-3). At the same time, Cleopatra also supposedly flaunted her wealth in front of Antony by having a pearl worth a tremendous amount of money dissolved in a glass of vinegar, which she then drank. She also is said to have filled Antony's chambers with rose petals, put on fabulous displays to entertain him, and give away a table's worth of silver plate as a gift after he complimented it. Famous people tend to attract stories that 'fit' their characters. So if Cleopatra already has a set of stories involving her use of poison and her party antics (especially those designed to impress Antony) then that makes one question whether this story, devoid of context and seemingly at odds with the rest of what we know, is true.