I agree, we won!
The one person who was pushing this (and really not being a jerk at all) concluded by saying he believed the 8 ball had to be made "clean". I'm really not sure what he meant. And it went no further as i simply said we called it off their ball. That was the end of the discussion. (By the way, I am 5'2" so I don't think I scared him.)
As you say there are many degrees of "no slop", indeed you could think of it along a spectrum where on the really crazy end you would need to indicate which side of the ball (in a combination shot) would have to make contact with the object ball --- call everything, really crazy. Or on the more reasonable end of the spectrum you, for example need not call short rails (i.e., "standard call shot"). Given that it was totally obvious that both balls would go in and that the eight hit their ball before going in (as called) his point that more detail was necessary seems petty and a tad closer to the "crazy" end.
House rules at the bar are "standard call shot 8 ball" last pocket, but since they had the table we said we would play straight 8 call shot as they were. That's all that was said about rules and I think that is the key here as you say.
From a common sense perspective, in the first place it would seem the purpose of calling banks, kisses, etc. is to prevent getting beat by some lucky person who really isn't as good as you are.
I grew up in a resort bar with about 6 or 7 tables where we played last pocket full on slop! You need only hit your ball first and make one of your balls anywhere. As a pre-teen we readily switched to their game if anyone complained about our luck.
In this case anyone could have made the shot i am asking about -- so luck is not the issue. But on the other hand maybe they thought they had the pocket effectively blocked and we should have been forced to bank the eight? They didn't say that though. At any rate this was something new and I thought interesting.... Thanks much, this is a very cool website!!! My first post.