been a while since I did and alignment on the honda's but I though you adjusted the caster by putting shims in the rod going from the lower control arm up to the front part of the sub frame? And the shims were at the sub frame?

either way caster does not cause tire wear but depending on how bad its out may cause a pull. Then the shop should have explained that. If they didn't I'd try another shop. Also always ask for a pre and post printout and if possible watch the guy do the alignment. I've worked with guys that would move the heads to make the readings right just to get done quicker.