That jibes with what a poster on here said was tweeted out of a newsroom somewhere, that it was a 7600, not a 7500 that was squawked.
I think you probably have the code #s reversed.
The explanation (by pilots) that I read said that he “briefly ‘scanned’ [stepped] through) 7500 [HIJACKING] on his way to 7600 [COMMS LOSS]”.
The encoder pictured showed four knobs — each of which sets a single digit —so, the brief error would have been in setting the “hundreds” digit..