I got this response from Matt and Tom:
There were NO votes from outside the country. This is a made-up claim.
We here at Survey Saint Louis would not accept outside the country votes,
for a NATIONAL Presidential , fun, little poll. Thanks for your concern.
I would like to see the original comments that Matthew apparently made where he wrote about the Canadian and Mexican votes. Does anyone have the link? I can't find it on the March Madness voting site.