I don't think that it's coming from the autobet feature of the website or casino where you are playing. There must be some other apps that you haven't noticed you downloaded and runs a miner into your PC.
I've met one of those miner when I did an entire cleanup to my PC and I've found it on my downloads folder. Take note that I'm not running the app and I've never launched it but it has consumed a space of my PC.
Try to do a cleanup with most of your downloads or apps you have installed.
The browser Maxthon was rumored to run a mining program in the background while their browser was open years before
this announcement was made.