Of course a woman-on-man thing can become rape, and by the laws of at least many Western countries, rape doesn't have to include "full penetration" though that's the first thing that comes to mind. I've read about recent rape cases (in the news in the last years) where it didn't really mean "forced entry", rather attempted making-out, tearing clothes off and trying (very close) to cuddle the crotch in spite of struggling back etc. This makes it no less disturbing to the victim of course, but it shows that rape doesn't have to mean forcibly plugging into the pussy.