My understanding (and I am not an aviation attorney):
* does the job appear on your pilot resume, or your employment history?
* was piloting a central or necessary part of the duties?
* did the job occupy any significant amount of your time?
* did the job generate a significant number of your logbook hours?
* did you get a W-2 from the employer?
* was it DOT drug and alcohol tested?
These are just a few tests that come to mind. There's no harm in erring on the side of caution and disclosure. I would think it more dangerous to fail to disclose a significant job than reporting an insignificant item to have it disregarded later.