I also took part in two stake.com surveys recently, so it might be related to those surveys as well. I am not sure, though.
Was the survey related to the deposit experience with fiat and crypto? Stake had sent two different surveys to all the users in the last two months. One of them was about the "St Patrick's Day promotions" and the other one was about "Super Bowl Madness experience". Your bonus isn't related to these surveys.
These bonuses are quite good actually, and they only send them when you are close to or past a level up.
I have never received such bonus. How much have you received from the bonus?