Out of band means communicated on different channels than ordinary information. For example a metric communicated out of band would be told to you in person instead of showing up on your universal agent smith react widget dashboard. :-)
Two different jargon phrases overlapping here, as I’m sure you know. Yours is “out of communication band” whereas GP is “out of predictive band.” Yours is a bit more common to me, but I hear both.
A band, on a metric, indicates a minimum and maximum safe value. For instance, if you alarmed when your latency is below 50ms or above 150ms, that'd be your band. Being out of band is being out of that 'safe' window.
It's a totally valid and common jargon phrase from the web services world, apologies though, I assumed that it was wider jargon than it turns out it is...
There's no language rule that a phrase can have only one meaning. You seem to be taking this too precisely, as the earlier explanations of there being two interpretations are quite entirely reasonable.
