Your friend's USB car port may be a 500ma port. Most of the USB devices (phones and vape mods) I've checked will pull 900ma or so if the charger can supply it and the device demands it. It all depends on the charger capacity and the current limiting resistor in the device being charged.
Using an outboard charger is probably faster and better for the batteries. Charging creates some heat and there's nowhere for it to go in an enclosed case except by heat sinking through the metal casing. Battery sleds are usually Phenolic, so a lot of the heat stays with the batteries.
Mooch says 2A charging won't hurt an 18650 as long as there's ventilation. If you look at battery specs, most say they can be charged at 2A max. My personal opinion is that 1A charging will probably lengthen their life compared to charging at 2A.