If the data is not processed at the edge, how is nothing recorded? This smells like extremely minced words.
IANAL (definitely not a German one) but I'm almost certain that even post-2017 it's still illegal to take video in a public space and send it elsewhere, without a sign, even if that video is not in some sense "preserved" elsewhere.
Frankly, I think you could even persist it to disk as long as it was pruned within 24 hours and reasonably say it’s not recorded.
Otherwise I’m not sure how you can argue ANY data is “unrecorded”. Writing to a hardware buffer in the camera module would seem like “recording” to me by the strict standard.
And I studied Film in Germany and had to deal with precisely this a hundred times. If WallDecaux is doing this, it is at least a legal grey area, unless they operate on private property, look at their own private property and have a sign that says there is a camera in operation.