The internet does have it’s wild west areas and there are many sites around which offer full premium themes from popular marketplaces FOR FREE.
Never upload these “free” themes to your host!
This is a blackhat concept of affiliate and spam hacking\marketing.
Those “free” premium themes are modified with backdoors.
Either they are able to generates an admin account and sends an email to the hacker with the logins or hidden affiliate links are injected to your website promoting all kinds of fishy programs.
It’s not smart to use something for free which is a commercial product with a price tag. The author does not get credits for his work and you take the risk to loose control over your website.