I am not a vet, blah blah blah.
I have seen similar conditions on dogs before. My previous dog had allergies in the spring and spots like that would show up where he excessively licked himself. Is your dog tending the spot or ignoring it? We gave our dog benadryl for his allergies but I don’t know what dosage to recommend for your dog or if that would help.
It could just be a bug bite like you said. If you can’t see anything there that is causing the irritation (like a stinger or pricker) then I would just keep it clean and watch it. If it gets worse or more swollen I would call the vet but I personally don’t think it warrants a trip to emergency unless it gets worse fast. Our current dog will lick a mosquito bite until it looks a lot like that. Or she will just scratch herself on something playing outside. But our dog is a rough-and-tumble dog who will jump around outside so small injuries like that are common, I usually don’t bother calling the vet unless she seems to be in pain or the spot does not have any improvement in a few days.
I wouldn’t worry too much, just keep an eye on it.