I don't "personally" think he was wrong.
BUT, part of the problem (and how they get away with this) is that there is no "official" language in the US. We are a "majority" English speaking country, but it's never been made the Official Language in the US.
Making English the official language is one of the things that I think should be in any immigration reform. Any immigrant, under the age of 25 (pick a number) and second generation immigrants should be required to speak English.
No, the prof should not have been removed for telling a kid what is in his best interest. In this case, learning the language of the country he resided in, and that’s English. What we have to stop doing is placating kids feelings. The adults need to start adulting.