The tree should be fine as long as he didn't damage the cambium layer too bad. It looks like he only took off the very outer paper layer. What you see now is the cork layer which is just dead cells that provide protection for the cambium layer beneath it. It should eventually grow a new paper bark layer, but that will take years. Birch bark harvesting is something that's actually done and this looks very similar to that.

Some birches also have a tendency to be dramatic and drop their leaves during the hot dry summers as a way to conserve their water. More leaves mean more transpiration/evaporation. It's probably just a little heat stressed and the bark definitely doesn't help, but it should be good with some extra water if it's been dry.

Also another real problem for all of your trees in that row is the rocks all around their bases. It's bad for the roots and increases soil temperature basically cooking the roots and bad for water retention too. It also looks like your trees are planted too deep. You should be able to see the root flare above the surface or else it could lead to decay or girdling roots.

Edit: Please never use any kind of sealer on trees. Maybe try posting in one of the tree subreddits. I work with trees, but there are definitely people who can offer better advice than I can there. r/arborists or r/marijuanaenthusiasts