Well, there are two kinds of introverts. Introverts by choice(this choice is normally due to the fact that the person is different from most of society). And Introverts who are introverts due to social anxiety/other fears.

People who are Introverts by virtue, tend to understand that some people are inherently introverted(because they themselves are introverted).

People who are Introverts due to irrational fear(like social anxiety) tend to think that all introverts are like them, and that all introverts would really secretly prefer to be extroverts.

If I had to guess, your therapist is the latter.

People try to help others, with their view of what makes THEMSELVES happy. Your therapist probably wishes he was more of an extrovert, but can't, due to fear. He thus thinks that all introverts are like him, and that they all secretly crave the same level of interaction he does.

In the end, therapists, like all gurus, are dangerous tools. Because they can just as easily lead you astray, as they can lead you to shore. The hardest part is, that as the "master", they are largely unquestionable. Most "students", or "patients" simply don't have the ability to tell when their masters(or therapists in this case) are wrong, due to the nature of the relationship.