D.M.
Hi J.----Not sure what it would be called medically but I think that this could be considered a type of scar. I don't think it would be permanent, but I wouldn't be suprised that it might take weeks, even months for it to fade. A fall like that put a lot of pressure on the skin and it was amazing that it didn't break it to cause a cut. A cut would scar...so...
Look for a product made by Burts Bees called Res-Q Ointment. Smells great, made with natural herbal products and is good for bug bites, cuts, bruises, etc. I use it for everything. Seems to aid the healing process. My dad has a scaly skin problem and this works as good as, if not better, than a prescription ointment. It may help to heal your baby's bruise faster.
I don't think it's anything problematic. It will just take awhile to fade. Ask the doc next time you see him. Be well, D.