But it's not appropriate to approach this the way OP did.
This was actually one of the reasons the Mod Thread was closed.
I don't see it that way. It doesn't matter whether the OP was correct about what was happening (he was) or the reasons it was happening (it looks like he was not). It's still an issue for all of us to be aware of. I can see where a mod might be offended by the post. But, I don't see a problem with an OP being offensive, unless it is intended to offended for the sake of offending.
Also, look at the outcome here. The issue is being addressed - mods learned that they were inadvertently doing something that caused problems, community members got an explanation (one that will stay here for people to refer to later, if needed), and efforts to come to a more permanent solution are in place. So, I'd say the OP did a good job.