Weird Google Maps Experience

I have a 2nd Gen iPod touch Black 8GB Model MB528LL.

I know there have been many questions from users pertaining to the Google Maps functionality and how it works in regards to WiFi networks. When I plan on going somewhere where I might need a map I usually open the maps icon and scroll around a particular area to load the map detail in my Ipod before I leave the house. This has usually worked out quite well.

Recently we traveled to a large mall on the other side of town to shop. When we left the mall I opened the maps icon to get a detailed map of the area we were in. Much to my surprise a blue dot appeared on the map and followed our progress as we drove through the suburban area that we were in. I checked to see if I was perhaps connected to a local Wifi - I wasn't. This continued for many miles as we traveled. The blue dot turned into a gray dot and stopped following our progress once we got into a less populated area.

Does anyone have an explanation?

For Houston, TX area people: I was at the Katy Mills Mall and traveled down Hwy 99 [Grand Parkway], my progress was mapped all the way past Westheimer and Ft. Bend Parkway.