There are 2 different advance purchase tickets.
The issue here is about discounted, US only, tickets.
the weekday ticket, which can be used ... on a week day ... obviously ... and this one IS restricted to US residents (canada and PR included, as per T&Cs)
The "any day" ticket bears no restriction as far as country of origin goes.
It's $80 though ... the weekday ticket is only $65 so I see why it will sound appealing.
Now what's strange, is that I made a dummy booking and the website will allow me to enter a foreign adress and even deliver outside of the US (even though I'd choose etickets to print at home)
I have never been asked for ID or proof or residency anyway.
But I'm someone who likes to play it safe, and would go for the $80 ticket or try to find a better deal.