Of course he did. That's what an incoming administration is supposed to do.
When was the contact, and what was it about? If it occurred just before or after the election, so what?
The problem here is (apparently) Flynn is saying Trump told him to contact the Russians when Trump was still a candidate not President-elect.
I’d go with the “Flynn is a known liar” angle at this point. And indeed, once a suspect flips to be a state informant or witness his testimony must be corroborated at some point.