Understanding "non-WAAS G1000" in a 2006 Turbo 182
The GTR345R is a transponder that can be purchased with a built-in WAAS GPS (link)—which this one apparently has. So it provides the WAAS GPS positioning required for ADSB. The GPS in the transponder does not provide a GPS source to the G1000. 

From what the shop said, it looks like the G1000 is an older version that is not WAAS capable. That’s probably why they chose to install the transponder with built-in WAAS since it was much cheaper than upgrading the G1000.