From what I read in the grievance, it seems like the complainant doesn't understand seniority. Taking a picture as a complete new hire class and showing up for the same Indoc events doesn't trump the fact that 5 of the 25 in that class started one day early. I've seen this technique used at another airline as well and it's done to comply with seniority, not abrogate it. The company wants to hand pick a few pilots in a class to train on a particular aircraft, they need to establish their seniority to support that - hence the early arrival.
Next time, the company will just call the 5 a different class to avoid any problems with semantics. Frankly, I'm surprised ALPA is supporting this one. It'll run it's course, use some of our dues money and in the end, they'll just hand the guy his coloring book and crayons and life will go on.