My 39m sister 24f says she was raped because a guy lied. Is this rape? How do I proceed?

At my wedding, my sister 24m met a friend of a friend 24(m). They hit it off. My sister lives about 3 hours from me, and she would come up to visit but also spend time with the guy. He’s in my friend circle (mountain bikes) and was contemplating moving across the country to work at another bike shop. Apparently they slept together, and he left that part out. About a month later he moved away. My friend told me that he almost didn’t move out, to persue a relationship with my sister. He was super conflicted, and in tears over it. I assumed it was over, summer love with two kids going in separate life directions.

Fast forward 6 months later.

Today, when I invited my sister up to visit she says all these things about “not being able to consent because he lied” , which led to “rape”, and that I should have protected her.

This was devastating to me.

How do I respond? i don’t want to dismiss her feelings, but I don’t agree with her accusations. I tried to stay out of the whole situation as much as I could, and treat her like an adult.

Is this rape?

What need other people’s take here. This is uncharted territory for me. Thanks.