Are the concerns about his shooting percentage being unsustainably high legitimate?
Yes. Xhekaj has played great and has had amazing success cleaning-up rebounds, deflecting pucks in, and more, but that shooting percentage is unsustainable.
Long story short, Xhekaj's been shooting from very high-danger scoring areas, deflecting pucks in, tipping goals, exploiting his very good shot in 2-on-1s, but he's also been getting lucky breaks more often than not from the goalies.
It doesn't mean that Xhekaj isn't playing great, because he absolutely is in these playoffs and the last 20 games or so of the season. But it doesn't change the fact that Xhekaj got gift-wrapped a couple goals more than pure numbers would have warranted statistically-speaking.
What those stats say in a quieter fashion is that Xhekaj played a lot of third/fourth-line minutes at the start of the year with Luke Tuch, focused on cycling, low-event hockey and possession, with not many shots.
It also tells a tale of improvemnt over time, only for Xhekaj to then get rewarded with PP time and more offensive minutes in which he found chemistry with teammates and got rewarded a lot for it.
Those stats also paint a picture that illustrates how Xhekaj has a tendency to defer too much to his linemates and should just shoot a little bit more himself, as well as Laval's situation this year of getting a lot of leads early, holding them, and then taking advantage of teams for empty-net goals.
There's lots of moving parts in this seemingly simple stat called "shooting percentage".