Lesson 8 provides part of Zhisheng's criticism of the Sanjie followers, who "practiced like Devadatta [and] established heretical Buddhism."

I assume this is referring to the Sanjie practicing austerities and begging for alms.

My recollection of Devadatta's attempt at schism was that it was motivated by a selfish desire to take control of the sangha.
I don't see any of that in the lecture notes, and would be surprised if these were the case.

Furthermore, I do not recall the Buddha rejected Devadatta's more restrictive practices out of hand or instructing Devadatta not to take them up, rather that he refused to make them obligatory.

That said, it would appear that a case could be made for the accusation of heresy in light of the Sanjie's innovation of taking refuge in five Buddhas and disbelieving in Sakyamuni.
However, given the dominance of Mahayana beliefs in China and the evolution of the notion of the trikaya, as well as the subration of the historical Buddha within the pantheon of Buddhas, including Vairocana, this position on Sakyamuni seems more of a logical result that a spontaneous heresy disconnected from the popular view.

In the absence of any additional information or elements to the story of Devadatta that I've forgotten or misconstrued, it would seem like the charges against the Sanjie are (seemingly typical for this period) perhaps politically motivated and may arise from the more mainstream groups' desire to maintain favor and influence with the emperors.