If I were to do a 50' swim in chlorinated water, that would be me for the day (and likely the following day). My eyes don't take to pool water very well. As you say salt water is a different matter though - I wouldn't have a huge issue with that.Based on the standards you quote, I would figure an instructor holding onto a student would not qualify as "swimming".
I know I wouldn't want to swim 50' in chlorine eyes open. Would actually like doing it in salt water.