The plug is usually topped off by a re enforced cap that's stronger and oversized to the tyre, the part poking through is I tiny bit of the plug or stem, glue friction and good old air pressure help keep the cap sealed firmly in place, the tyre construction has a webbed material running through it which the rubber is bound to, the underside Glued side of the cap holds this ruptured area firmly in place, this type of repair should not be confused with the old web and glue emergency type that just pushes through the tyre from the outside and is designed to just get you home or to safety
