That's because Deng Xiaoping wasn't General Secretary or an official leader until 1983. From 1976 to 1978 the CCP was led by Hua Guofeng. The leadership within the CCP post-Mao and pre-Deng was frankly chaotic. With the Gang of Four post 1973 seizing power and their subsequent losing of it in October and the "trial" (quotes because it was clearly a procession as opposed to an actual trial) in 1981, Hua Guofeng was the man who was by title still in control and was acting as Chairman of the CCP.

Note that Chairman of the CCP is abolished in 1982 after Hua Guofeng is replaced by Hu Yaobang. Deng's policies don't really come into prominence until the late 70s where his power is solidified with the outmaneuvering of Hua Guofeng gradually from 1978 to 1981. Incidentally though Guofeng was in charge of the Trial of the Gang of Four in 1981 most of his power had faded due to the consensus of the CCP to move towards a more conservative and less Maoist stance on leading the country. Spearheaded by Deng Xiaoping, Hua would basically fade into obscurity given his strong stance and favor towards original Maoism.

In other words, Deng had solidified his power base post-1977 and by the 11th Meeting of the CCP in 1978, his power base within the less Maoist members of the CCP rallied with him and the majority of the party went with Deng's policies. It also must be remembered that Deng was a prominent CCP member even before the death of Mao in 1976, though he was purged by the Gang of Four in the Cultural revolution Deng had prior to 1978 a rather strong power base considering the chaotic and erratic nature of the Cultural Revolution.

The book Deng Xiaoping and the Transformation of China covers this pretty well, I think.

In the annals of world political history, it would be difficult to find another case where a person became top leader of a major nation without formal public recognition of the succession. Before the work conference, Deng was vice chairman of the party, vice premier, and vice chairman of the CMC. After he became the preeminent leader at the Third Plenum, he was still vice chairman of the party, vice premier, and vice chairman of the CMC. Not only was Deng not given a coronation or an inauguration, there was not even a public announcement that he had risen to the top position. What peculiar combination of circumstances had created such an unusual situation and what were the consequences? At the time of the Third Plenum, Chinese leaders wanted to avoid giving the impression to the Chinese public and to the rest of the world that China was undergoing a power struggle.

They decided, then, not to give him all the titles and to balance his power with that of an equal, Chen Yun. The strange arrangement of giving Deng authority without formal recognition worked because everyone knew what was going on, and because Deng himself was more interested in real power than in any formal job title. He readily accepted his responsibilities on an informal basis, without demanding public display

The 'power struggle' the author is referring to was a struggle over the general direction of the party. The two sides to this struggle were led by Hua Guofeng, Mao's chosen successor, and Deng, who was criticizing Guofeng's 'Two Whatevers', which was a declaration to follow Mao's policies. The 'Two Whatevers' were, in part, why Mao chose him to succeed.

"We will resolutely uphold 'whatever' policy decisions Chairman Mao made, and unswervingly follow 'whatever' instructions Chairman Mao gave"

Deng represented the faction of leaders who understood that Mao's policies had failed miserably. Many of them, like Deng himself, had personally suffered under them. They didn't want to be beholden to Mao's policies, and they didn't want to have to deal with people who would criticize someone who deviated from them. Deng instead championed an essay titled "Practice is the sole criterion of judging truth" - not Mao's little red book. He swung this politically by criticizing followers of the "Two Whatevers" for not conveying “Mao's true spirit, which is to seek the true path from facts.”

The reason why the transfer of power went so smoothly, and without the need for Deng to take over the biggest titles, is because, as was hinted at earlier, Guofeng didn't really hold alot of power. Marshal Ye held the military, Deng had influence in the military and the state, and Chen Yun the economy. Marshal Ye was the effective 'kingmaker' in this scenario.

Marshal Ye believed deeply that the errors of the Great Leap Forward and the Cultural Revolution had been caused by the excessive concentration of power in the hands of one person. He urged both Hua Guofeng and Deng to work together in leading the party and the country. When Ye met with Deng, Deng agreed that they should strengthen the collective leadership and limit the publicity given to a single person. Hua too had accepted Marshal Ye's advice to yield on the content of party policy and to accept Deng as the preeminent party spokesperson. Without any public celebration, then, Deng accepted Marshal Ye's advice to prepare for his new role, even as Hua Guofeng retained his formal titles as head of the party, the government, and the military.

That hints at another reason why Deng didn't receive all the pomp and circumstance: Marshal Ye didn't want another supreme leader. To a certain extent, Deng didn't either, though he did end up pushing Hua out entirely, and when Ye died, Deng took over the military, effectively becoming the PRC's most powerful leader in history, after Mao.