An extremely brief tweet, using an unnatural construction (new player of) and a spelling mistake (verry), doesn't prove his ability to speak English.
I watched his AVTV interview (which was all in French). He said that he is looking forward to learning English.
Granted, that doesn't mean that's not his Twitter. I think it's highly unlikley though.
It's really basic - he could easily have written it. As he's French, he most likely studied English a bit at school, so he probably knows a little.