As has been stated here, it is very common for pilots to misidentify aircraft in combat. 

That’s one thing.

Likewise, as I have said repeatedly here, I can understand a corporal thinking (or wanting to believe) that the victorious Germans were aiding a supposedly inferior enemy who was about to conquer them.

So lets go back again, to the original post and the mention of the Singapore Germans in the book “WW2 in colour by Stuart Binns and Adrian Wood”.

In what context was it presented?

A corporal isn’t exactly on the command staff, so anything he wrote isn’t the product of accurate Intel from H.Q.

Did the authors mention the corporal’s comments as an attempt to illustrate the mental state of the soon to be defeated garrison?

Or do they expect the reader to think they are presenting some new hidden piece of history?   If so, we have a problem.

As I said, even primary source information can be wrong…no there were not a sizeable number of German pilots flying for Japan….but it would be useful to study the rumors and apparent paranoia among British troops there.