I don't know if you have to think it is true, but it most certainly is something you have thought about. Maybe it was a drunk thing, and a sober Mel Gibson doesn't think Jews are responsible for all the wars in the world. However, the fact he is blurting it out tells me that it is something he actually thinks about. That already makes it an issue. How many non-anti-semites actually think about whether Jews are responsible for all the wars in the world?
This is not the booze talking, because booze doesn't accuse Jews for war. It really only happens with people who think in those terms in the first place.
I had a sort of related event last weekend (booze related, but nothing illegal). Was at a class reunion, had a few drinks, and brought up my opinion that one of my classmates was the ugliest person on the face of the earth. Dang it, she was and still is absolutely butt-ugly. She doesn't make up for with a great personality (probably pretty average in that regard), but that's off the point. Looks-wise, ugly. Objectively ugly.
Probably wouldn't say it sober (although given the crowd, I might), but at 0.12 or so, that stuff comes out. But the connection here is that it is something I have thought about before. Hell, for 25 years, I've thought that, but didn't say anything to anyone until now. The point here is that you don't spout out stuff, even when drunk, unless you've thought about it previously to some extent.
So I don't know if sober Mel is really anti-semitic, but the thoughts have gone through his head. Meanwhile, my classmate really _IS_ the ugliest person ever.