I think you've missed the point of what I was saying. We've been stealing from them for years, invading their bases, taking their probes (which may well be Thargoid children for all we know), we've destroyed millions of their scavenger drones (all of which are completely non-hostile until you attack). It seems likely that we've invaded their space. That's where my analogy of the guy on the subway comes in.
Yours suggests a totally random unprovoked warning from a random guy. Whereas the reality is that we've been aggressive and hostile to the Thargoids for years, so them warning us to back off before attacking as a last resort is exceptionally laid back. So your analogy is flawed because it doesn't take into account the history you might have with the subway guy, hence my correction to include the precipitating event.
The aggressive hyperdictions are an anomaly it's true, however it seems likely to me that they are retaliating against some people. I've personally flown all over the Pleiades and encountered the Thargoids dozens and dozens of times and I've never had a hostile hyperdiction. It seems likely to me that it's possibly a reaction to something, like maybe the fact we're blasting them apart en mass. Or, alternatively, this fabled second faction that are more warlike.
As I said, which you ignored, I think if the roles were reversed and the Thargoids had been doing to us what we've been doing to them then our first 'live' interactions with them we wouldn't warn them to back off first, we'd go in guns blazing and try to find ways to kill them faster. Because that's exactly what we are doing, and anyone calling for a more reasonable approach to assess the situation more rationally is being shouted down pretty aggressively by the pro-kill-them-all camp.
You're right, Occam's Razor is indeed the case, and in this case the simplest explanation is that we've been invading their space and playing with their toys and they're justified in laying out some ground rules.