Earlier quoted context omitted.
This bug, which continues to cripple HTML5 apps on the App Store but not ones accessed in Safari, seems almost too perfect to be unintentional.
But Safari doesn't load local files, so the bug wouldn't be noticed there. Makes perfect sense.
I don't doubt that there is probably an explanation that makes sense, but based on what we know, the least malicious explanation is that they forgot to test WKWebView with local files, which doesn't make sense.