You should take legality with a grain of salt. Most of these rules in practice apply to things that are wide-spread, such as sharing an entire game on the internet (or rather, a website sharing many games on the internet), not to a single person downloading a rom from a site or uploading some game files from it.
Even taking that into account, countless people upload games onto the internet without getting into legal issues over it.
The worst that can happen is that your file will be deleted from the file host you're using and very maybe accompanied with a cease and desist from the respective company (which doesn't make you a criminal, it's literally just a notice telling you to stop what you're doing before legal actions will be taken).
If you were really that keen on legality, you should realize that a lot of what happens on the site isn't exactly legal. It's moreso a grey area but it's certainly not entirely legal.
Even taking that into account, countless people upload games onto the internet without getting into legal issues over it.
The worst that can happen is that your file will be deleted from the file host you're using and very maybe accompanied with a cease and desist from the respective company (which doesn't make you a criminal, it's literally just a notice telling you to stop what you're doing before legal actions will be taken).
If you were really that keen on legality, you should realize that a lot of what happens on the site isn't exactly legal. It's moreso a grey area but it's certainly not entirely legal.