Alex will be polite and respectful to the Thessyx, but will NOT be able to hide his curiosity about them, their biology, how their society might work.
He'll answer most questions they have for him (minus anything specific about his family members like names or what cities they live in) and try to ask a lot in turn.

When the critters show up, he'll ask them if they know what the critters are and/or have any experience dealing with them and what they recommend to do with them.