Sonderkommando Lange shown on footage in 1939/1940?

Recently, a documentary about the Nazi extermination camp Kulmhof was shared (Polish and English) on YouTube. In addition to current footage of the former Nazi extermination camp, the documentary also features contemporary photographs from a permanent exhibition. At minute 1:43, a German officer and three soldiers with a motorcycle sidecar can be seen in front of a building.

 

The English caption reads:

"Members of the Sonderkommando Lange in front of one of the buildings of the psychiatric hospital in Dziekanka in Gniezno, December 1939 - January 1940."

The photograph is thus a unique piece of contemporary history, depicting the mobile Sonderkommando Lange (i.e. before Kulmhof) during an operation.

If it shows what the caption suggests...

 

One may question why a killer commando that otherwise operated under high secrecy would openly appear like this from the beginning while being captured on camera.

Or why Lange would use a motorcycle with sidecar in the first place. It's not as though the Gestapo in annexed or occupied territory wasn't motorized with larger horsepower.

On the other hand, it could also be the Luftwaffe number plate of the motorcycle or the Luftwaffe officer's uniform, indicating that this is more likely a photo in the context of the Luftwaffe reserve hospital in Gnesen rather than the deportation of inmates of an asylum by the Secret State Police. 

Last but not least, the scene doesn't align with what witnesses of the operation reported:

"The first transports of patients were picked up in the winter of 1939/40 by an SS command using ordinary trucks. At that time, the institution had approximately 1100 patients. It involved two or three trucks."

 (interrogation of Bogdan Orlicki of 21 June 1971, BArch B162/17388, ca. p. 2073)