Not at all strange. It's common around the world for airlines to act as a contract lounge for other cross-alliance airlines where there's no suitable same-alliance lounge available. As you've said, there's no suitable *A lounge for those airlines that doesn't involve either a 2nd trip through security, or a very (very) long walk (and obviously even that option is only new with the new connection between T1-T2). At the end of the day, CA/AF are happy to take money from their competitors, and lounges are a profit center when used like this!