The system is designed around the honor of players to actually do what they say they will do. A good person who signs as a tank will play as a tank. A person who doesn't care about others/the raid could sign as a tank and just use a dps spec or stand in the corner afk.
Doing any of this isn't an exploit.
Random guess, but did you have your pet out already when entering the raid finder instance? It is possible you are still using an old UI that now causes crashes because it modifies the Pet UI.
Yep, it is really annoying and happens to me all the time too.
Open the Challenges UI to see what the challenges are and what they are all about. If you are using a custom UI and don't see the button for it, you can go find the hotkey (Shift+C)?, or just get the updated version of the UI if/when it is done, or revert to Original UI.
As for the TSW-> AoC crossover thingy mentioned in that TSW update/newsletter, that was only talking about a pet they copied from TSW now being available in AoC in everyone's claims window as a celebration of TSW anniversary. That pet will be removed from claims in a few more days, so you better go claim it on each character before it is gone.