I suppose with those specs, it should be some other process that's actually negatively affecting your system, or that the wolfbet autobet feature just takes up that big of a process, mainly due to the auto bet codes they have. That or a malware got in and is pretty much eating up you're CPU processes by hiding behind other online processes. Since you also used Ubuntu, which I said I have not much knowledge of, the numbers you're seeing right now might have been capped at a certain limit, hence why it's huge. The cap isn't necessarily the maximum amount your pc can handle, but rather the maximum amount your browser could use.

Anyway, one things for sure, it isn't them mining in your pc. Try doing a hard format, or just cleaning up tempfiles and the like. Scan your pc as well for possible malware, and if the issue persists, try bringing it into a professional and let them take a look at possible issues your pc may have.