I don't know what happened to your chameleon, it could indeed have been too much vitamin d3 from the supplement, but the sunlight did not hurt it in any way regardless.
Chameleon bodies stop making d3 from sunlight when they have enough d3 already in the system. The d3 can be either dietary or produced from exposure to sunlight. Either way, they stop making it from exposure to sunlight when they have enough in their system already. They *cannot* produce too much d3 from sunlight exposure. That is why it is more safe to use real sunlight and no dietary d3, than it is to use the dietary d3. Dietary d3 can be overdosed, d3 from sunlight, never can be.
So if the dosage of dietary d3 is not excessive indoors under artificial lighting, it cannot be excessive outdoors under sunlight. The only reason dietary d3 is not used when outdoors is because it is unnecessary. It isn't because an appropriate level of dietary d3 in addition to sunlight will cause an overdose. That would be impossible...