It's computing it straight from the GPX file, with no filtering or attempt to tone it down. Nearly always reports a higher number than the GPS itself does (which, in most cases is a little low, IMO).
Try the 'climbing analysis' dialog to try some different things (and sources of data). More stuff along these lines (including more accurate elevation computation from DEMs) coming soon.
Right, GPX stores elevation in meters. You can overwrite it with DEM data if you want, or use the data recorded by the unit (what's there now).
