That's correction from Stake, means the first code contains the wrong amount and the new code give you additional amount to fill the missing amount in the 1st code.
So basically it is not a bonus for a specific event, just a correction amount.
Yes it is not the first time, it has happened several times already and it shows the honesty from Stake to their players.
Ah I still have doubts like something is wrong my total wager this week is $3k usually i get weekly bonus between $12-15 but this week seems to be doubled as you can see in this screenshot , do you feel this week's bonus is more than usual? ah whatever it is anyway thank you stake we are waiting for moments like this in the future