Of course, this is not legit at all what they do. Now, I can not detect if their themes are clear and without any malware, since I have never used them and never will, but chances are that they have edited them and added some kind of backdoors and in the worst scenario they can completely hack your site and do anything with it or in the best scenario (for you) they can “just” place invisible backlinks and do other hardcore black hat stuff on it for spamming purposes.

The fact alone that they post them for free means that they need to somehow make money, because they clearly are not a charity.

The only logical scenario you could use them is when you are 100% confident that you can remove any possible backdoors and you will use them only on for testing purpose to see if they are a good fit for you and if they are, then you can buy them from a legit source.

If you are not very good at coding to spot any nasty code in the files, then you should never use these nulled themes unless you really do not mind having very bad things happen to your website.

It is a custom made theme for WordPress, at least it looks like one. XWPThemes had for sale a clone template of the PornHub that looked similar but for some reason, they stopped selling it, maybe it is just temporarily, you would have to ask them about that.

They seem to be self hosting their videos but it can possible that they have coded their own plugin like the KenPlayer that hides the original source, so I am not 100% sure on this one.

But I am sure that they have done lots of custom work on this website and no one is selling (legitimately) the copy of it.