Could be a little bit of how the driver adapted, and a little bit of how the track was laid out.
Like I've said before, on a relatively smooth track with fast, long radius turns, the Z06 should just walk away from the competition. On a tighter track, it'd fall back.
And the Gallardo does have the advantage of AWD on slippery or low traction surfaces. This does wonders for lap times if the driver has trouble controlling the other cars on the limit.
And tires. You never know what condition those damn tires are in... or the humidity, or the dust, or blah blah blah.
And yeah, looks like they suck at driving manuals, but from those times, looks like they still got the other cars to 60 (96) in under 4 seconds.