That's correct, Dick, the US does not currently require a TSO146 - or any TSO'd actually - position source for ADS-B.So long as your GPS can be recognised by the transponder or UAT, you're good to go. That being said, you cannot use a non-TSO'd position source for separation as we can here, and that has recently been mandated somewhere, IIRC.
Your mate has been told a bunch of horseshyte. You do not need a TSO146 GPS navigator for ADS-B, you only need the position source, being the GPS puck itself. Naturally this us usually incorporated into a navigation reciever like a GNS-430 that then feeds the ADS-B transponder, but it is not required. You can install a stand-alone ADS-B transmitter if you so choose, for perhaps 5-10K.