It was known for about two minutes that Frink was banned before he posted. I assume it’s just some technical glitch that allowed that to happen.
Oh.
When you’re banned, they restrict access to your account so you can’t log in (speaking from experience). I imagine adding someone to the Banned Users group is a separate step in adminCP compared to restricting their login. So maybe he knew (and posted) because there was a 2 minute window between them adding him to Banned Users and blocking his login access.