Should I call it "Markin his territory"???

My middle child Collin, who now is 8 and in 2Nd grade is my most observant child. He almost has a photographic memory. I say almost because it's actually like selective hearing. He only likes to use it if it's for his own benefit. I would say to him "didn't I tell you, you couldn't leave the yard" he would say "no, I don't remember you saying that" or "I told you a hundred times not to ride in the street and to wear your helmet" his reply would be "I don't remember you telling me a hundred times only a few". Okay, so he’s got me there.
Well, the summer before he went into kindergarten we started to prepare him by telling him little things like how much fun he was going to have and how many new friends he would make. Basically, all the fun and positive things you can think of telling a child to get him excited and ready for the first day. Then, about a month before school started we found out that our neighbor who lived right across the street and who we all liked very much was going to be his teacher. He was so excited to have Mrs. M as his teacher and we talked about it everyday how lucky were. Finally, it was his first day of school and after much separation anxiety on my part I waved good bye and then watched him settle into his class with ease.
So, 3:00 came around pretty fast and it was time to pick him up at school. As soon as I saw him I started asking him questions one after another on how his day went and he answered them with enthusiasm. I was so happy he liked school and had a great time. As we approached our street Collin said “my teacher Mrs. M lives across the street from us”. I remember him saying this because I thought it was a little strange he asked me that because we discussed it all the time he never forgets anything. But, I blew it off quite quickly as we pulled into our driveway. When we walked in the house he asked to have a snack and then asked if he could go out and play and off he went. I watched him go out the front door and after maybe a minute or two later I looked out the window and I saw Collin in his teacher's front yard. As I was watching him, wondering what the hell he was doing over in Mrs.‘s yard and so soon after school I saw him pull down his pants. I think I was in shock because all I could do was watch. I didn't think to go to the door and yell at him I just watched. I remember as if it were yesterday. He pulled his pants down all the way, to his ankles and because the rest of him was so tan from the summer his bright white butt cheeks lit up her front yard like the fourth of July. Then, I saw him separate his legs, pushed his belly out and he just started peeing in his teacher's front yard. I fricken watched in shock as he finished taking a pee, shook it off and pulled up his pants. Then, he just turned around, ran back into our yard and around the side of the house to the backyard and hops on a swing like nothing ever happened. What the hell was that??? Could he actually be marking his territory??? I guess I'll never really know but, I have a funny feeling it was a warning of things to come.