Verizon's network has been live for quite a while now and there's a decent number of customers actively using it. I would wager there wasn't many other AT&T customers sharing resources when these tests were conducted, but on Verizon's there was.
I'll be curious to see these tests repeated in six months, a year, etc.
(NOTE: not a Verizon fan... I'm with Sprint... just pointing out the obvious).