Yes, there was a reward. If I recall correctly, it was a mimic metamorph wand. You get it by playing the content and doing the quests or raids and they would grant a beta token and if you collected enough (not sure what the exact criteria but several), then your account qualifies.
doing one with a Dev gave you more, but iirc you still got some if you finished a raid, or for unplayable ones because of problems if you reported specific (non-lag) problems out on the forum.
I'm pretty sure the hidden Beta Reward is that the entire game population gets to continue "beta testing" the content through 2021 until the next expansion launches. You all act as if they've got a long demonstrable history of responding to beta information. They don't, and it will be demonstrated over the year by posts of general population players complaining about this or about that, and then a beta player will post how "they knew about this or that in beta, and they did nothing." Nothing new here, but by all means enjoy your mimic wand while pretending it was all worth it - I know to some of you it will have been thus.
When did it come out last year? Tried to forum search and could only find a post that said someone told them it was in claim.
I think it's typically around the beginning of March. I could be wrong though, I never really pay attention to the exact date.
I see mine, but fellow guildees are reporting not seeing anything atm. So it may take time to get em all out.