non-profit usage is called when it is used by government, public administration, non-profit organizations, church, schools, or similar.
If you use RIOT in the process of creating commercial video games, this means a commercial usage.
I will replicate here the answer given to a similar question:
if i use it into the company, could it use it for free?
The license states among other things:
Free License: The license for this version of the Product requires no payment by the user to The author or any other party.
However if you do enjoy it or use it in your company, please consider a small donation to the developer for his time and efforts to make this software possible and support further development.
This means, yes, you could use it for free in your company, but in this situation I expect a donation, since I’ve put a lot of work in this program and you use it to help your business. This is simply a moral issue. Nobody is forced to donate, but a symbolic donation from companies would be appreciated, to let me continue development and support my expenses.