I don’t understand what the narrator of the following true story means. Can you clarify?

Here is the narrator’s story:

When my brother got married, I was like 16 at the time. I was taking high-school exams and that’s why I couldn’t attend my brother’s wedding party. He had this party in another city, and I was home studying. I knew he and his wife would come back home late at night and I tried to stay awake while they come back. As you may also know, we have these mattresses that we sleep on, so I put three mattresses in the living room, one for myself and with the distance of about two meters I put two mattresses for my brother and wife to sleep on. I didn’t have much knowledge about marriage and all that and I didn’t know if I should put their mattresses next to each other or not?! So, I took a risk and kind enough to put those two mattresses next to each other and mine was about two meters away! Imagine that! Also, keep in mind that I didn’t have any knowledge about sex, marriage, and all that!
:D
So, they came back home late night and I said, I know you’re tired and want to sleep, so I put the mattresses here. Both laughed and my brother said something like, “what is this? No, it shouldn’t be like that.” I said, why not? They said, they’ll take care of it.
Days went by and this horrific news got passed by to others and my mom heard about it also. About a few months ago she told this story again to someone and said poor Mohammad doesn’t know what marriage is, and I realized oh my gosh, she still remembers.