Does not seem like they specified whether it was browser or desktop teams, but either way it asked him to install an actual system package which you should never do anyway.

The relevant part is:

* they scheduled a meeting with me to connect. the meeting was on ms teams. the meeting had what seemed to be a group of people that were involved.

* the meeting said something on my system was out of date. i installed the missing item as i presumed it was something to do with teams, and this was the RAT.