"Because of its many biochemical processes, yeast also contains a number of sulfur compounds. Under certain conditions it can release a couple of fairly simple ones into the beer: sulfur dioxide and hydrogen sulfide. These are the two that tasters are most likely to describe as simply “sulfury,” but they are quite different in character. Sulfur dioxide is the pungent odor of a just-struck match or spent gunpowder. Hydrogen sulfide is the rotten-egg or volcanic gas aroma."
Some foods that have a sulfur smell: Onions, garlic, eggs
Some supplements that have a sulfur smell: Alpha-lipoic-acid (ALA), Glutathione (GSH), N-acetylcysteine (NAC)
So it was probably a yeast that fed on the nutrients in the sweat. Terbinafine has a high biodistribution so it also reaches the skin in the armpits.
There are chlorophyll-based chewing tablets which are used orally if you ate something with garlic to neutralize the smell.
Topically used it should have the same effect. Just did a quick search and found chlorophyll cream and soap.
I doesn't necessarily mean that someone has yeast in his armpits it could just be something genetic where your sulfur excretion over the skin is very high.
I always get that onion armpit smell when I eat onions. :p