Is this really offensive or am I being over feminist here?

Today I had a meeting with a client whom my colleagues (men) warned me of that he is aggressive, however, he turned out to be quite nice to me actually and it was a good meeting, when I got back I told my colleague of that, and he directly responded that client was nice to me because i am a woman. Is that sexist? Why did he assume so and did not consider that I may have been able to communicate in a better way that gave better results?