IF you try to make the wall flat with the tile, it's not uncommon to end up with a gap at the edge where the tile stops.
WHat's a bit more troubling to me is that you can see gaps underneath the tile from the edge! Ideally, the tile would be 100% supported, and you'd see no gaps. If he used the same technique in the rest of the shower, it is a bigger issue. FWIW, neither tile nor grout is truly waterproof...in a shower, even if you seal the grout (that's more for staining than waterproofing), there will be some moisture getting behind...If it's fully covered with thinset, it won't accumulate, and will tend to dry out. If there are gaps, it can accumulate and even run out in areas you wouldn't expect. In a wet area, industry standards call for 100% of the edges, and 95% of the rest of the tile to have thinset coverage...no where near that, at least on those visible at the edge.
If there's a matching bullnose, you can make it look decent when painting the wall. Won't address if there's some other issues, though.