OP, I think you're onto something. What you laid out seems reasonable to me. I don't really follow HS running (and, funny enough, didn't even when I WAS a HS runner) so I can't weigh in on posts and pictures. I don't know what any particular guy at NP looks like. So here's what I'm wondering - it seems to me he was doing one of the following:
1. Still 'on the team' in an administrative sense. If you went into the school office or athletic office or somewhere, there are names written down of who is on the XC team, and he's there. However, he doesn't train with them nor maybe even travel to events with everyone else. He may or may not have their uniform, but if he's on the list, probably does. I suspect this is what the OP is leaning toward.
2. Technically 'on the team' according to the school, and very much on it in every way. Obeys the coach, wears the uniform..... nothing's changed. If this is the scenario, the SM stuff has been confusing (I, like the OP, think something's there) but he's just one of them like he's always been. I feel various posters believe this is the situation.
3. Not on the team. Not on any list in any school office. Won't be in the team picture in the 2023 yearbook. (This describes me my Senior year.) Still a student at that particular school, but so are hundreds of people not actually on any school-sponsored sports team. I submit this could be the deal. Possible. I don't know how likely. However, I don't follow all this closely enough to know if, for example, he has an official uniform....and/or has been to regular-season CIF-sanctioned meets, arriving on their bus, wearing the uniform, and very much part of the team at the time.
Variations exist. Here are some:
#2 was the deal for the entire CIF season. Therefore he was 'on the team' for any school-sanctioned events. But at the end of that, which I suppose would be the State Meet, nobody is technically part of any official school team since none existed anymore. Ergo, #3 was sort of the case during the meet in question (NXN, I believe), but that is misleading because he'd still appear in the yearbook picture and on any official list, having participated to the extent the school allows.
Similar to above but #1 describes the 'regular season.' This seems likely, and is what the OP suspects as far as I can tell. Still, I guess everybody at NXN is #3 in at least some sense since no official school-sponsored team exists other than during their sanctioned season (or so I believe, not being much of a high school sports scholar).
Starting the season in #2, just like he did last year and before, then jumping to #1 after seeing the coaching and training situation....this is probably the most likely scenario. Why wouldn't he simply sign up for XC like he did the last few years? Realizing the coach is gone, or more accurately, what that truly meant, he may have just told himself that 'practice' was now a waste of time. Perhaps the new coaching staff tolerated his independent training and didn't remove him from the list nor demand the uniform back.
So, what's the deal?