Being called "white trash" is not racism. It's an insult. Racism goes way deeper than just name calling. It's being denied a decent education, housing, job opportunities, and other basic human rights and priviledges only because of the the colour of your skin.
I'm a black South African and have experienced both direct and indirect racism. Do I think Silva is racist? No. Am I offended by his post? No. Having said that, he should have known better. If he wanted to make a private joke with a buddy of his, he should have kept it private.
One thing I will say is this though. The cartoon character looks nothing like Mendy. The only similarity is that they are both black. And that's where the problem lies. Maybe not for Mendy but for some people. On some level, Bernardo is aware of Mendy's blackness. That's not a bad thing because Mendy really is black. But there are people who have been discriminated against exactly for that reason: someone was aware of their blackness and used it against them in some way. The result is that they have become SENSITIVE to it. You may call them snowflakes, soft or whatever. But unless you have experienced real racism, you are in no position to judge how the people who have respond or react to certain things.