His account is verified, so he did tweet those things, however very nice of him to apologize even though he don't really need too. Not often you see that so kudos to him.
He has his opinions and can hold to them. The fact it goes against Barca and Catalunya hence the reason for his contract termination is another matter, but he don't need to apologize for what he believes even though he could convey his message a bit more professionally.
All in all, the club should learn something every competent entity knows and does: Background check.
That's it.