You are really lucky. I have tried playing on slots with high RTP like that several times, but I have only won big once, the rest have been losses. Perhaps my luck has just been really bad lately... maybe I will try again next time 
Yes it was unexpected luck, and as I said, I managed to make 2x withdrawals in quick succession. I could have even done it 3x, but I got too comfortable playing. Now the RTP has dropped dramatically, so it's better to take a break for a while.