It could be he's just being cautiously optimistic. It sounds like he's trying not to have too many expectations at this point and just seeing what happens. I wouldn't think too much on it at this early stage.
I should admit I am an overthinker but while my post may come off as me being concerned - I am not. I'm just going with the flow, and will throw it in the next conversation it makes sense "Hey so when am I buying you lunch? Thursday or Friday? " I just bring all of my silly over thinking thoughts here for my fellow SOers.
Oh I totally feel you. I'm the queen of overthinking!
I overthink too. I'd just see what happens and if he doesn't contact you, you could always reach out to him a little later on. Hopefully he contacts you!