It doesn't take any fancy machine learning to figure out what is happening.
The most striking example of those massive rebounds is the account of @AdelAliBinAli. Before the purge, this account had 6.2M followers. On July 14, its follower count was down to 2.7M followers (-3.4M / -55%). Between July 14 and July 19, it regained 1.2M followers, and as of July 23rd, this account now has 6.6M followers, which is even more than before the purge and represents 3.9M additional followers gained.
As for the others, having more than a statistically average number of purged followers is evidence that you were buying fake followers in the first place. The obvious explanation for large increases in followers for someone who is already known to buy them is that they bought more.