Do you have an app connected to the Ecobee?
Are you using the Ecobee with Amazon Echo?
Both of the above allow the unit to determine location and other info via your smartphone or via Amazon's loc service.
Regarding how the ecobee3 determines location for weather I did find this under ecobee Support:
"Weather Station
ecobee Support
posted this on September 12, 2012, 4:04 PM
Q: I live in a mountainous region in New Hampshire, and I'm wondering which weather station the thermostat will connect to (valley or mountain)? Around here, this makes a big difference.
A: The weather forecast is determined by the address you use to register your thermostat. From that address, the ecobee determines the latitude and longitude coordinates. The thermostat finds the closest weather stations and then uses an algorithm to interpolate the data, based on geography, to derive weather for your (very specific) location. The ecobee will then take several closest weather stations in your area, run an algorithm, and estimate the weather at your house (as opposed to a single location - i.e. airport)"
So it looks like ecobee3 determines the geographic location for their weather forecast from the ecobee product registration address.