Well, he gave you the wrong glue. You could have tile come off the wall over time as the adhesive you're using is specified for vct tile which is a product you normally see used for school, gas station, grocery stores, hospitals flooring...etc. You can either A: keep your fingers crossed and pray the tile stays or B: remove it all and reapply with tile mastic.

Not sure how long the tile has been installed but you have a good chance of the product drawing out the moisture in the glue too fast causing it to not cure properly. More than likely the tile will come off the walls over time.

I let it sit a few days before applying grout and many of the tiles have started sliding down. I am going to pull them off and do it again with mastic. Thank you for your help.

You're welcome and good luck with your new install.