How Can I Tell if My Colleague’s Code is AI-Generated?

I'm currently collaborating on a React project, and my co-developer seems to be advancing quite rapidly. However, I've noticed that many of the files they're writing are quite large and poorly structured, with issues like bad component separation and an excessive number of useState hooks. This has made me suspicious that they might be relying on AI to generate most, if not all, of their code. Are there any tools available that can help me scan our codebase to identify files likely generated by AI? I really want to understand the best approach to take—should I be enforcing certain coding standards or asking them to stop using AI altogether? I'm eager to get your thoughts on this.