It's a tough call, it all depends what's meant by aggressive, who was saying it and why they were saying it. Does passive aggressive count as being aggressive ? how about laying guilt trips, is that considered aggression ?
One could make an argument that a personality type who's prone to regular old in your face overt aggression isn't the personality type who'd resort to not eating meat for moral/ethical reasons. ie cruelty free reasons.
I've run across that statement in a feminist, anti-VAW context before but never "in general"
I agree that 'aggressive' is a difficult word to use there. This was a report on some research someone had done but I doubt it was a "set in steel" scientific research project. A magazine article, perhaps. I doubt it would stand up in court although I am suddenly remembering the twinkies case that stood in court in San Francisco years ago. It was just something that struck me as interesting in regards to eating or not eating meat.