I doubt they are using illegal methods to catch people. If they were, it would be 100% ban rate, which isn't the case. They will not kneejerk ban based on an IP address. That said, whoever said that it will raise extra suspicion is correct. If they have 100+ accounts logging in from the same IP, it may cause extra scrutiny on their part.
The bans will have some human interaction to avoid false positives, hence the delay for some people getting banned. It is ridiculously easy for Blizzard to pull a list that would be close to 90% accurate based on hours played, gold earned..etc. We don't see everyone getting banned because blizzard obviously has some human interaction in the actual ban reviewing process. Every additional thing you do that fits the profile would make your account a low hanging fruit for whatever team works on this stuff at blizzard.
Just common sense to avoid other things that would show up on an automated trend report. Just my 2c.