It's a good point, and is probably because you've downloaded high-res terrain data for that area. The elevation in the airspace stack must be the maximum elevation under your finger, because that's what any airspace AGL is based on. However once you go into a precise coordinate, we will show you the precise elevation at an exact coordinate, if it's available.
An update to What's Here later this year will make it clearer that there is a difference in the type of elevation being displayed.