[JoanneF]

It's not really possible to say - a bump on another dog might look similar but have been caused by a completely different thing - particularlysince you aren't sure what caused your dog's lump.

I normally keep an eye on lumps - if it's just a sting or bug bite, or caused by knocking into something it might go away. But if it doesn't go, or if it gets worse, then I'd see a vet.