Has nothing to do with whether on target or not. As
@FatBloke explained, every shot gets an xG value based on where it's taken from and under what conditions,
not based on whether it's on target. xG basically measures the quality of the chance, not the outcome. So when you look at a scoreline you can get a sense if a team got lucky with their chances (low xG with many shots, but scored a couple of goals), or pretty much scored what they should have scored (e.g. had xG 2.5 with 5 total shots and scored 3 goals).
Wolves had an xG of 0.69 from 20 shots and none of them had an xG rating higher than 0.1. So their best chance had a 10% probability of going in. In other words, they hardly managed to scare us. Just because one of them happened to be close to the post doesn't mean diddly.