Is this reason to call things off genuine or an excuse?

I had been seeing this guy (he is 29) for over 3 weeks - we met on a dating app and really hit it off since the first text exchange. That in itself has been so rare for me and when we met in person, I had a really good feeling about him. I’m 26 right now and of all the dates I have been on so far, some of the best dates were with him. Since the get go, he was very thoughtful, playful, great with communication - all qualities I generally seek in a partner. We spoke on multiple occasions how we both intend to have a long term relationship out of this.

Everything was going great until yesterday when he mentioned that he had been thinking about something I told him the other day. It was a conversation about how many kids I see in my future and it wasn’t a very serious conversation. But I essentially told him that the idea of pregnancy scares me because I experience really bad, painful periods every month. He brought that up yesterday to tell me how he sees many kids in his future and if that’s not what I want, we should call it off. I tried to clarify that I see kids in my future too and what exactly I meant by what I said to him the other day and that we basically are on the same page about it but seemed like he had already made his mind.

I didn’t force him to give this a try because we weren’t even in a relationship yet and he seemed pretty sure about ending things but I just couldn’t understand his reasons despite me clarifying that we are on the same page about wanting kids. I feel shattered right now even though we were only seeing each other, that too, only for a few weeks but I genuinely felt that we had something (which I haven’t felt for anyone in a really long time). The thought that’s harder to shake off is what he said merely being an excuse because if he were genuinely interested in seeing where this is headed, he would have at least tried to understand what I meant by what I said? Instead, he just made up his mind based on that one sentence that I casually said out loud in a random conversation.

I don’t know what to make of this but I just wanted to get an opinion about what this seems like - a genuine reason or an excuse?