Why did he go cold after our date?

So I went on a date with this guy I met online about three weeks ago yesterday. He was the one who initiated everything - set the plans, picked me up, chose the time, everything. We drove around in his car, he even gave me his phone to pick the music, and at one point he wanted to send a selfie of us to his friends or brother (not really sure which). He paid for my food, and after dinner we went to this lookout spot where you can see the whole city. The vibes were really good. Then we kissed, and things went a bit further. He seemed really into it, maybe more than I was. I didn't exactly want to go that far, but I didn't say anything at the time. After that, we cuddled a little, but when he was driving me home, he got super quiet-like completely different from before. I even asked if everything was okay, and he just said yeah. When we got to my house, we kissed goodbye, but when I waved at him after getting out, he didn't wave back. Later that night, I texted him saying I had a really good time with him, that I hoped he got home safe, and that I was excited to see him again... but he didn't reply. I'm honestly pretty confused and don't know what to think. Did I do something wrong, or is this just how some people act after a date? If anyone's been through something similar or has any advice, I'd really appreciate it.