If this happened to me, I would absolutely ask my T why she gave me the extra stone and what she was thinking when she did it. I would also probably mention the part where I felt like maybe she was being competitive with my partner or maybe she was threatened by the affront to her geological knowledge, etc. All of it, even though I would probably make zero eye contact as I said it.

I say the "if this happened to me..." bit because these situations are where my T really shines, when we can kind of pick apart something that happened and what she felt and what I felt and what I thought she felt. I'm rubbing my hands together with glee because in these moments I am often so very wrong, and it shines a giant spotlight on the things that keep me psychologically distressed. I don't know if every T works this way, but I'm delighted when my T and I can really dig into an incident like this.

That said, it's possible that he's just beyond excited that you showed even a tiny interest in his totally geeky hobby. There are one or two topics where my T and I share an intense interest in something, and I can see her excitement and extra willingness to share pop up occasionally when those topics come up in session. It seems like good technique to highlight similarities for bonding purposes, but I think it can also just be the excitement of connecting with somebody over something that's important to you.