There are no stupid questions! Only stupid answers, perhaps coming from me.

From what I understand from all of the reading I've done here, it seems like it's a combination of both conditions and it being "time" to molt. Crabs can and will put off molting, to some extent, when they're in poor conditions, and it definitely seems that when they leave the store and are placed in a nice crabitat, many are ready to finally get down to business! Of course, sometimes crabs molt even when conditions are poor, with poor results in most cases...
But yes, from what I've read, I think there seems to be a tendency for them to molt fairly soon after leaving a pet store because they've been "putting it off" until things were more comfortable! So yeah, I would think that was a good sign that they like their new home and that conditions are good... though the real sign will be how successfully they get through the molt!
good luck, and I hope this helped! Again, I'm new, so anyone should feel free to tell me everything I said here is wrong and post your more educated opinions.
