to be honest, I think this simple method would catch a lot of bots.
i don't think so, partly because of what i said above, another factor is that the follow for follow mentality is very strong on twitter, some ppl will follow back just about anybody without actually checking the account
have you checked those followers? i just did, the vast majority are real ppl for sure, the real to fake follower ratio is nothing out of ordinary
the relatively sudden increase in his followers count you mentioned above happened because of different reasons:
1. he followed 1k users fast (and you noticed the acc right after this before the wave of follow back kicked in)
2. follow for follow mentality no matter what
3. those peeps followed back the acc too who actually checked it and were curious what will happen, i'd simply call these the victims of his reverse psychology
4. occasional bot accs, but not higher than the average which are present in every user's followers
i'd go further

, maybe you can find more bots among those accs who he followed, but don't or won't follow him back
what he's doing is definitely working, not because the acc was intended to catch bots, but because he's trying to get followers, at least in my opinion
if i were to notice this user first and if i were to post it here, most probably i'd give a different title to the thread, something along these lines would have been more closer to the truth:
"How to get a better than average followback ratio on twitter"