Offline Maps and Data Usage

I'm an Android convert from iOS. Just got a GS3 last week and I love it so far. One of the things I love is how much better the stock Google Maps application is than the one from iOS (and I'm not talking about Apple's jacked up mapping app, I'm comparing it to the "old" Google Maps for iOS). Anyway....one of the features I was excited to find was the ability to cache maps for offline use. After caching a map of the area where I live, I tried a little experiment.

Before leaving work yesterday, I input my home address into the navigation app and downloaded the driving directions, then turned off my phone's mobile data. Everything worked seamlessly during the 15-minute drive, even without a data connection. I was pretty excited about it, but I wanted to test if Google Maps was smart enough to use the offline/cached map even when a data connection was present. So this morning on my way to work, I checked my current data usage, then input my work address as a destination. On the way, I noticed the "4G bars" moving/flashing, but figured that could be email, syncing, or some other background function that required data. When I got here, I checked my data usage and it had increased by 2MB during the short drive. I confirmed this was all from Google Maps by filtering the data usage down to just today, then looking at the "per app" statistics.

So why did Google Maps need 2MB of data to navigate me to work?

1. Downloading Driving Directions? Considering how fast they downloaded over 4G, it couldn't have been more than a fraction of the 2MB.

2. GPS? It's my understanding that GPS doesn't require data at all. And my test from the day before kind of confirms that.

3. Downloading Maps? Hmmm.....I can only assume that Google Maps will only use the offline maps when you don't have a data connection available. I guess that makes sense, they are called "offline" maps after all.

Can anyone confirm or deny this suspicion?

Thanks in advance.