Both "opinions/theories" have valid points, IMHO.
But, I will take exception to the notion that nest guarding males won't "EAT" an intruder. I've site fished nesting Bass & Crappie (in clear water) ... and had them attack my lure, hooking them deep in their throats. They didn't just bump it with a closed mouth, to drive it away, or nip at it to send it fleeing. They had every intention of removing the threat, by the most logical method at their disposal ... eating it.
And salt may not have much of an "odor" ... but, it does have a "taste", and salt impregnated plastics do have salt grains that are exposed to the water, so it is feasible that the fish can "smell" it at close distance or taste it when inhaled.
(ever hear of a guy known on the web as "Senko Sam" ?? )
... cp