Seeing how the water acts on the tile surface I think they must have applied some sealant to the tiles beforehand. Which is a good practice before doing epoxy grouting on tiles like that, BUT they should have made that clear. Working with ardex products daily I can tell you that leaving epoxy grout on unsealed tiles like that, for one hour you'll have a HUGE problem.
can confirm. one of my contractors had to wet sand epoxy off a porcelain tile. he even cleaned everything pretty well, but shoulda done a final wash with clean water. tiny amounts left on the surface but a horrible haze/residue
