The only reason this is even a discussion is due to the SB and the "accidental" observance of a anomaly not related to the SB. (This rivet location is not what the SB calls out to inspect, correct?). What if this was in the next bay over?
Please don't get me wrong. I admire the thought process of not being satisfied until you are sure. However, I don't think a definitive answer will be discovered. Die penetrant may not be conclusive gouge vs crack. Many have viewed the photos and none of us familiar with seeing cracks feel this exhibits the typical tell tail signs.
Far better to err on the side that a problem exists, but I see nothing wrong with satisfying the SB with observance at the next interval, be it the annual CI or more frequent inspections if you feel they are necessary. I inspected my HS several times the first year that SB went into effect, but after a year and nothing changed, it became a CI inspection once a year.