What do you mean by public area? I just tried to reproduce it, and while all posts and the like given and received happened in a category limited to TL0, the user was promoted.
Are you referring to personal messages? I don’t think those are included in TL2 requires topic reply count as messages aren’t topics. To me, it makes sense to exclude them; otherwise, they could easily be abused by two new users to get a higher trust level without interacting with the community at all.