Khabib cheated repeatedly throughout his career.
Look at his last fight before joining the UFC. His opponent was a regional journeyman with 20+ losses and Khabib still felt the need to cheat by grabbing the ropes to prevent a takedown. He did that in prior fights as well.
In the UFC, he cheated by shamelessly grabbing Tibau's shorts to try to stop takedowns. Khabib also cheated repeatedly on the scale. He missed weight against Trujillo. He no-showed the weigh-ins with the interim belt on the line at UFC 209 against Tony Ferguson because he was overweight. Khabib eventually would only fight in Abu Dhabi without an athletic commission, so he could do sham weigh-ins.