Issue with Altitude

Interesting issue from a user with an EDGE 1030plus. He grabs interesting routes from RideWithGPS, downloads the activity FIT file, imports to Garmin Connect, and uses that to drive a trainer for an indoor workout on the route.

You can see the RideWithGPS route for the first 10 miles on the right. The elevation data in the profile.

On the left is his ride data in Garmin Connect. The native ELEVATION is shown in grey, which matches the RideWithGPS elevation as expected. However, I write what my data field gets using the "altitude" from Activity.getActivityInfo(). It is not at all correct. It can't be the barometer or GPS, or it wouldn't vary from 200 to 1300 indoors. Any clue what is going on here? I get valid altitude data outdoors.

He also ran a field called "Sensible Grade" (by flyingflo) which does seem to work. I'll try to reach out to they person to see how they gather the altitude in this use case.