What’s your thoughts?

I’m 18 and dating a 22 year old. We’ve been together for 1 year and 4 months now. We both still live with our parents and are trying to save up for our own house! My boyfriend was out of town working for 2 weeks so once he got back, we got a hotel room so we could spend some alone time together. My mom was kinda upset but she got over it. His mom suggested “If she wants, she can spend the night at our house.” So we took up that offer and I spent the night at his house and slept in the same bed as him. My mom ended up texting me while I was at his house and said this...(I posted a screenshot)

So my question to everyone is...who was in the wrong? I’m technically an adult since I’m 18, so I feel like I should be able to spend the night at his house if I want, as long as his parents are fine with it.

Also, there’s more to this story. His mom even mentioned that if me and my bf get married anytime soon, but don’t have enough money for a house yet, we can both live in their house and have a room just for me and him. When I told my mom that, she completely freaked out and got mad. She walked away for a second then came back and said, “To me it sounds like they’re trying to make their son legal.” My boyfriend is an immigrant, he has permission to be here and work, but he’s still not “legal”. So my mom is thinking that his parents want us to get married so he can become legal sooner. It really hurt me when she said that. They’ve never done anything wrong. My mom loves my boyfriend so I don’t understand why she would say something like that. Me and my boyfriend don’t want to get married until we have our own house, but I still don’t understand why my mom would say something like that...