nüRoute™ trafficTrends™is not the same as real time traffic messages with a GTM receiver for TMC (Traffic Message Channel).
Traffic Trends is historical data collected by Garmin users and uploaded back to Garmin during map updates like when your using a nüMaps Lifetime map subscription.
If you have enabled the Traffic Trends in your unit and checked the tick box in Garmin Map Updater, then you actually transfer your contribution to the Traffic Trends statistics.
Traffic Trends quality is just relying of that the users have their units on at most of the driving time. More samples and more roads driven by users gives improved data. At every new map release you will get more statistics in the Traffic Trends DB.