Being a fungus, it may well travel via spores in the air. Not sure about that one. I don't know how long it lives without a host either.
I'm not sure I'd be talking Boof out to other places or letting him say hello to any other dogs until it's over. But then again - where did he get it? The vet who told me my dog had ringworm - told me "don't tell anyone" and we kept going to dog school though I cut back on the meet and greet. There was a dog with spots at our local park - that probably gave it to her - if that's what it was.
But you don't want to spread it around or share it if you can avoid it. I hope the Great Dane lady washed up carefully after looking at Boof. Or maybe Boof got it from the Great Dane lady who got it from her dog? Who knows. But if her dogs have the exact same thing - you may want to keep clear of her and her shop until she gets treatment for her dogs. Did her vets test for ringworm?