It's possible to say that you aren't making a recommendation, while you actually are making one.
Trump was asked a question, and he answered it. I don't think that's a bad thing. I disagree with his opinion on this, of course, but he has the right to express it and come out in favour, if you like, of one position or the other. But the language of Brexit supporters over Obama (or, recently, on anyone in the UK having an opinion on Trump at all, from some on this site), suggests that they were very unkeen on anyone from outside the UK expressing an opinion on the upcoming referendum. The question is whether this extends to those expressing opinions in their favour also. The answer, it seems, is "no".