Jenn, while I have no doubt whatsoever about what the Rangers told you, and I see the same thing here in Colorado and Wyoming about the Rangers not understanding the fire bans (and there is really no excuse for that), alky stoves are specifically banned currently in Yosemite/Seqouia/Kings Canyon. Esbit stoves, which I personally think are the safest, aren't mentioned but the allowed stoves statements doesn't include Esbit. There's probably a low chance of being fined for using an alky/Esbit stove, since the Rangers don't even know the rules, but you can indeed be fined for it.
No smoking and no building, maintaining, attending, or using a fire, campfire, or cooking fire (including charcoal fires) within Yosemite Wilderness or at the High Sierra Camps. Portable stoves using gas or pressurized liquid fuel are allowed. Alcohol and "Sierra" stoves may not be used in wilderness under these restrictions.
No wood or barbecue fires permitted at any elevation. Gas or propane stoves are permitted at all elevations. Alcohol stoves are prohibited.