I mean it has been a long time since I saw the episode but I thought he came off as quietly exasperated and despairing rather than skittishly panicked. This could come down to bad acting the actor may have just been unable to convey the mood.
If he's not that worried then why would he try to prevent Picard from giving them passage he can just breed more. Is he worried about people leaving or not? He's worried enough to lie (apparently in an obvious way according to you) to Picard, but it is not actually an existential threat, this is a pretty narrow keyhole of worry he is in.
Note it is not clear that they can just breed more it is unclear what kind of development process residents of the place go through, but to me it seemed implied everyone was born and grew up at a normal human rate, no fully educated and functional quick grow adults churned out here. So it might take 20 years of maturation and educating the next generation to replace them. As I said way back in this thread one might say that makes no sense as the colony from the same era in Up the Long Ladder did have quick grow clones.
I mean I think your response illustrates a point, it is difficult to discuss this episode because as shown in this thread people have so widely different takes on what was portrayed in this episode either because of bad writing (Picard seems both to think the colony takes away what makes life worth living and lament its destruction), bad acting (how worried is Conor really?), bad world building (like discontinuity with similar backgrounds in the setting)