If the PM was sent from your account then your account does deserve negative trust, regardless of the IP. It's trivial to use another IP so you can't prove it wasn't really you. And even if you account was really compromised then it deserves negative trust because it can be compromised again.

I've asked OP to prove the PM is real. If it is then I'll tag you too. If he doesn't prove it after some days you could ask vod to remove the feedback he's left on your profile