Still does not explain where this "to the foot-precise" altitude or height comes from. ADS-B/mode S rounds to the nearest 25-feet, surfaces movement radars are primary/2D radars. FDR - RadAlt seems a very likely source, but this data shouldn't be available to Flightaware and neither so soon ...
Regarding the deconflicting, depends what they had in mind when designing the system, rwy incursions, etc. yes, wings clipping at the gate, most likely not, twy incursions 'from above'... probably neither....