Sanded versus unsanded is based on the width of the grout line:

1/8" or greater, use sanded.
Sanded has...ta da...sand as a bulk filler to minimize shrinkage cracks in wider joints.

If unsanded was used in a wider-than-recommended grout line, it's not a guaranteed recipe for disaster.

If the grout does shrink and crack, it'll usually flake out of the joints as well. Some have simply regrouted over the cracks to fill them in. It's a band-aid approach. It can work. Or it may not work.

The better bet is to remove the grout. I've only had to do it once. I used a diamond bit in a dremel-type of tool. Dusty, dirt.

the tile guy said he used an additive to make it strong. let's hope it holds up.

Most grouts are already modified.

In this case, success will bear more on the amount of water used to mix the grout. The more water he used, the more likely you are to get shrinkage cracks.

Fingers crossed!