Measuring buildings from the sea level is odd... I didn't know that they did this anywhere?
Here in Germany it's usually everything upwards of the street level, that is measured/considered as height of a building. Here in Germany but also in other places in Europe the height of the eaves/the lower edge of a roof/top edge of the façade is also a big thing, since many building regulations, like in Berlin, determine a maximal height for the Eaves in certain areas etc. (In Berlin its their infamous 22m "Traufhöhe"/eaves height) Those things are also measured from street level.
I thought that was the usual way to measure those things...
Imagine Madrid or Zurichs "fake" Skyline with measurements being from sea level, both cities being more than 600 and 400m above the sea ... Goodbye Dubai
When I draw or I request buildings I try to get hands on some sections or elevations of the buildings (which isn't always possible) and measure those things in CAD. If they divert more than +/-0,5m from the database I put them on my list to submit corrections at some point if I manage to finde more verifiable data...