Child's Nasal Issue after seeing his dermatologist yesterday?

My son has a wart on his right nostril where the nostril meets the septum. He's had two cryo treatments so far to get it removed (he's 4) and will need a 3rd next month for hopefully the last time. His first appointment went smoothly. This time (an appointment yesterday), the only difference was the use of topical Lidocaine an hour before to try to ease some of the obvious pain. So the dr was able to really get the wart this time with less fear of hurting my boy. This morning, my son's left nostril showed signs of a nosebleed. He blew his nose and bloody snot came out. It isn't ACTIVELY bleeding, but when I look in the left nostril, the septum wall is a darker color...looks like it's bruised almost. If it wasn't a Saturday, I would have already been at the office asking them. He isn't in any pain, not acting different so I don't think it's anything serious. That's why I'm just coming here. Thanks for any feedback!