I just played a match against a person who had two legendary minions. They didn’t discover, excavate, or anything that would allow them to find another random minion.
I was pretty sure that you only get one legendary per Arena draft. How is this even possible?
If people could somehow hack whatever cards they want into arena why would they only do 1 extra legendary? Some random Legendary isn’t even the best card to hack in if they wanted easy wins. You missed something.
You probably missed something that summoned a random minion to the board and that random minion just happened to roll legendary. Like a Crystal Broker played on 10 mana and rolling a 8 cost legendary as its random 8 drop.