I would guess a few things. Could be wrong viscosity oil, could be something left disconnected in the induction system while checking the air filter, though this would set a code and CEL. They may have set your tire pressures too low as well.

In the future if the person doesn’t understand something as basic as high mileage oil, take your car somewhere else. They don’t have the knowledge to be qualified to be dealing with cars if they don’t know what high mileage oil is.

That’s what this is. Most pads are painted on every surface but the friction surface, some even have overspray there but it’s NBD. The paint is just burning off from normal brake heat.

Run. Run far far away from it.