More surprised that theverge is using word "leaking", when it should be "sending" or "reporting". Leaking, make it look like an accidental behaviour.
The feature they're referring to is configured remotely [1] with a set of domain filters that demonstrate the intent was to only capture a subset of sites. I think this is where I'm now supposed to refer to Hanlon's razor--Never attribute to malice that which is adequately explained by stupidity.
[1] https://www.bingapis.com/api/v7/followweb/getdomainfilter?ap...
If microsoft really wanted to scan ALL urls that badly, they can... always just do exactly that? But when they actually implement fairly decent feature that has a bug in it... it's probably a bug yes. They really have no reason to be sneaky about it