That post had like, a very poignant criticism on the entire loop 'genre'.
I mean, if you want an example of a not off-topic post, that would be it. And if you want an example of a not useless post, in terms of actual story criticism and not just a masturbatory wank-fest, that would also be it. It's the complete opposite of 1:2.
The fact that the original poster didn't want to stick around to push that point is like, quite irrelevant, and in no way invalidates the actual content of the post. Call it a drive-by critique. It's entirely valid.
Additionally, supposing that it is off-topic, and supposing it is useless, deletion is still unwarranted. 1:2 explicitly lays out that only in cases of extensive threadjacking will the posts be moved into their own appropriate thread. Not a single post thought. And not deletion.
Heck, if we want to talk about 1:2, off-topic and useless posts are in fact allowed in moderation. So, if that's the rule that was broken, then that wasn't the rule that was broken.