You don't know that, actually. They might have taken a mediocre application to a good one, but it's not about the quality of your applications, it's about the quality of the application relative to others. And a professor doesn't know what other applications they're getting. But it is useful information to know that a professor is enthusiastic and communicative.
Anyway, my signature line seems applicable here. Congrats on your acceptances; don't let them go to your head. Getting through grad school is pretty difficult if your entire cohort won't talk to you.
This will vary wildly based on the specific department and person.