Context: a guy has invited his girlfriend over to study, and the girlfriend finds a dirty magazine. The following exchange takes place:
男 : 香奈さん? 今日はテスト勉強しにいらしたのでしょう？
女 : 何が勉強だし! どうせ千秋はこういうことばかり考えてたんでしょ！
男 : そんなこともないけど…
Why did he say も here instead of saying そんなことないけど or something similar? I can't quite figure out in what sense the particle is being used. It doesn't seem to me a case of it being used in the sense of "even," or trying to show how big of a thing something is. It also doesn't immediately make sense to me for it to be in the sense of "also"; in that case it would mean "that's not the case" (in addition to other things not being the case), but the only way I can make that make sense is if I assume what he means is "I didn't invite you over for that, but I may not have invited you over to study either."