Does your Garmin also refuse to say anything until you pass the first sign, and also stop indicating the speed limit if it's been a long time since you saw one, and also from time to time pick up spurious roadside signals as speed limits, indicating 70-100 MPH in 25 MPH zones, and also finally does your Garmin stop indicating speed limits if you cover its forward-facing camera with a piece of tape?

I think the clearest indication that Honda Sensing does not use location data for speed limits is that Honda Sensing is available on cars that don't have GPS at all.