I haven't really looked into these problems before, but the FAQ says:
A tag synonym is usually a tag that has exactly the same meaning as some other tag
I see a clear difference between pythonic (complying to good Python practices and style, "idiomatic") and just being related to Python.
The same faq answer I linked to also states:
There is no tool for correcting a bad synonym. The only recourse is to post a question to Meta Stack Overflow explaining the problem with the synonym relationship. If enough people/the correct people agree, the site admins can make the change manually.
That's why I'm posting this.
P.S. If I'm wrong and the synonym is correct, I'd still like to know a way to search for pythonic questions (although I guess I can't search for a tag synonym and not the master tag).