Unfortunately normal. The particular issue you see involves the factory weld spots of the exhaust piping. The exhaust pipes are made of a mix of alloys that do a nice job resisting corrosion (stainless steel being part of the composition). What you see at the welded connections happens when the welding material used isn't identical to the exhaust pipe material, or the flux used during the welding process didn't protect the molten weld from oxygen well enough to maintain alloy uniformity. You see this phenomenon often when corrosion-resistant materials are welded. While normal, it will be a location of both internal and external corrosion acceleration relative to the rest of the exhaust pipe, and is possible to prevent. That doesn't mean this will be the first spots of failure though. Likely where gasketed joints in the exhaust piping are used, those joint flanges will be made of mild steel. Those are usually the first to fail. Plus places where water settles (if not driven long enough to flash off condensation) will cause failure (such as in the bottom of the mufflers and resonators).
Probably a little too much here, but I'm not aware of any vehicle manufacturer that does a decent job with welded exhaust piping joints.