It Must Just Be A Bug, Right?
Edge has found a new way to usurp your browser of choice, at least if it is Chrome. There has been no official documentation of this change, nor did Microsoft respond to Ars Technica’s inquiry about the new behaviour so we could assume it was a bug, if we wanted to be nice. It seems tied to the Edge feature which offers to import your recent browsing data from Chrome, which it does every time you launch Edge unless you disabled it. From recent reports it is possible you will start seeing that offer again even if you did turn it off previously and even if you did Edge syncs your Chrome browsing automatically.
This was noticed by several users who noticed that after a reboot the desktop had an Edge session open with all of the tabs that were open in Chrome previous to the restart. You should be able to disable this completely by opening edge://settings/profiles/importBrowsingData and toggling it off, however the people who noticed this bug had already done so. We await a response from Microsoft to determine if this was unintentional or yet another attempt to force people to use Chredge.
Without an official comment from Microsoft, Warren posits that the tab-snatching happened because of a bug or an inadvertently clicked-through dialog box that triggers a feature in Edge that's meant to make it easier to (intentionally) switch browsers.