They don't up/down ranking individual sites for stuff like this. They've probably implemented back-hijack detection for the whole web

I just added a screenshot from search console: https://dejanseo.com.au/competitor-hack/

There's no manual penalty notice.

They de-indexed the domain. I think they do do this on an individual basis from time to time, especially with sites distributing (links to) illegally obtained content.

They didn't down rank it, they delisted it just like they would delist child porn or copyright material after receiving a dmca notice

I've read otherwise but couldn't find anything with a couple min free time. Anyone else read/know about this?

That would be marvellous.