This may not be a useful inquiry for you, but I find it curious you didn't ask him to repeat himself, as in just a simple "sorry, I didn't catch what you just said. Can you repeat it?" No need to tell him what you'd heard possibly mistakenly or react to the correct information.

I guess the curious part for me is why you wouldn't want to know what he actually said, rather than an assumption, particularly in the context of the session topic related to autism. It was an assumption in the first place by you, in the sense that you assumed your former T gave you accurate information. In some ways it is perfectly reasonable to rely on what someone tells you about another person, especially when it would seem she received that information first hand because they once worked together, but in other ways you can't, just like any other "gossip" about somebody else.

I guess I just wander if there is something there in your communication style that may bear examining, given how much being clear about what you're saying and being clear about what the other person is saying is so central to human relationships, including T. And whether being less clear in speaking and understanding others could be connected to feeling anxious about the relationship or other kinds of issues.