I'll double down on personality that parent comment pointed out. If you see someone submit a project they worked on instead of formal education then you need to see what their exact contribution is and how they interact with other devs. Look at past github comments, issues, etc. Lurk in their chat server or pull logs. Expect to see a more casual attitude than what will show up at work, but pay attention to how contributions are handled, how credit is handled, and how disagreements are handled. It's not a universal problem, but I've seen some of the worst developer drama around volunteer open source video game projects.