Sorry to hear about your frog Whether store employees know what they're talking about or not, they're never really trustworthy. It's like they're part of a chain petstore where they know nothing, or they're at a specialty store that assumes a lot of their customers probably know the basics and that they don't need to go over the little things. It's not your fault; you looked for the correct info and were under the impression you had it. Frogs are just so much more sensitive than most reptiles that husbandry mistakes can kill them very quickly.

If it makes you feel any better, it sounds like he was probably either dead or beyond being aware of things by the time he went under the chameleon light. Hopefully you found this stuff out in time for the other frog though.