It's possible that the shop wanted to get rid of some of the thorn resistant tubes. I only recommended them when it was appropriate to do so, but my shop hated carrying them because they were so hard to sell.

Besides that, if it WAS a defective tube, a non-defective standard tube should have been a sufficient replacement. There is a significant performance penalty in using thicker tubes. They do not deform as smoothly as a standard tube for easy rolling nor do they leave as large of volume of air for cushioning impacts.

If you value performance over puncture resistance you went the wrong route.