That's terrible that the fish croaked.
A simple risk evaluation put it that there would be more than usual morts on the trip. Nice of the guy to fix a problem that he was not responsible for.
I'm very surprised too. I even told him it was that crap airstone from walmart that caused them to die and 23 of them in other tote lived. For some reason he feels obligated to replace all 50. What a guy!
I don't think he feels obligated, but is just a nice guy!
Your probably not the first he's dealt with that had a bad rig, and probably would like to see his fish thrive for you. He's just a nice guy.
I would suggest to bring some extra cash with you to cover the fish you killed in your desire and haste excursion. He offered to cover this, but you reciprocate and and admit to your fault. A good way to build a friendship.
Remember, people like this are not Walmart!
Good luck!