What to Expect on a Call with a Startup Founder?

I'm a third-year computer science student and recently had an unexpected thing happen. I've been contributing to an open-source project to learn more about coding and real-world applications, focusing on fixing bugs and understanding how production systems operate. Then, the founder of a company based in Europe reached out and asked for a call. It sounds like he's interested in learning about my background and possibly seeing how I might fit into their team.

The issue is, I'm still quite new to this, and I haven't worked in a startup or production environment before. Most of my experience comes from personal projects and some hands-on tools I've built.

I'll be discussing my:
- Background
- Approach to building things
- Potential fit within their organization

I'm hoping to get insight from those who have experience in startup interviews. What kind of questions should I anticipate from founders?
Especially considering:
- I'm still a student
- I caught their interest through my open-source contributions
- I lack formal work experience

Also, what should I prepare beforehand? What key qualities do founders usually seek in early-stage engineers? Should I brush up on particular technical topics or concepts? Any advice would be greatly appreciated since this is my first opportunity like this!