PN received, thanks again for providing this information. Please stay tuned, will review the info next week and give some more background afterwards.
But basically the reason why this is happening was explained in some text in between previously:
The current SSH implementation is working in a way that it requires such systems not having a full linux shell available to be detected as such. As an example you can find the implementation for the HP iLO devices initially reported at around line 400 in the file gather-package-list.nasl.
Something similar is most likely required for this second system as well.