Possibly, but I think it's more likely to be things like
--germinating weeks to months later than indoor started seeds because the soil has to warm first.
--more effort in putting roots down in compacted garden soil rather than a loose potting mix.
--no transplant shock to the roots, so primarily depends on the long tap root, instead of a larger fibrous root mass closer to the surface which can absorb nutrients more effectively.
If it was just the freezing, then people who keep seeds in their freezers should also have weaker plants. You could theorize that there might be some borderline point of freezing moisture in the garden where the embryo is not killed but has some damage, though.
You could test this by digging up and moving the volunteers into another spot in the garden or transplanting into a large pot and see if they develop differently. Of course you would have to treat them really well so they could catch up with the earlier indoor plants.