You should have had him take the bike home, so YOU would have to fix it tonight. Honestly, as with ANY skill that you're trying to learn, just watching someone else do it is practically useless. You should have already changed the tubes in both tires at home when you have time, BEFORE getting a flat out on the streets.

The only tricky part is to make sure to get the glass out; sometimes there are bits remaining after you pull out the obvious bit.