Except they didn't give it to me, my partner/sibling/parent/friend did, in a message sent through their app. We should expect that kind of interaction, to not be tracked; should expect, but obviously can't expect it today, these news are not surprising.
This is just one more aspect of their tracking that may be non-obvious, and that it's good to know about.
Regardless, i don't consider it to be acceptable behaviour by Instagram to inject their tracking into all web pages i access through their app just because they can.
Android has a nice universal "back" button which can close an opened tab and return you the app that spawned it. iOS tried a similar option with a "go back to App" link at the top left, but it doesn't fully close out browser tabs spawned by the app. Safari has gotten smarter about this, with browser "back" buttons closing spawned tabs in many cases, but not all.
So, in all those emails where I click to launch a browser to "read more" but see no reason to keep it around, the embedded browser actually plays a maintenance role: no need to get rid of those tabs that were just a funny comment I wanted to see but never need to keep.
Yes, the tracking is disappointing, but the UX of not having a zillion tabs open (and in old iOS version, hitting tab limits) makes my life easier.