Well I can’t see anything wrong with that post. There are other shorter thankyou posts on the (rather interesting) thread, and even multiposts in a row in a short time span from the same user (this could also be a cause for post deletion).

I wouldn’t overthink it too much. Recently I has a post deleted on the B&H thread. I couldn’t figure out why, but all in all it is just down to having spent around 10 minutes in vain in that case.