I don't think it was random, I happen to have a Colombian passport and I use VPN's on a regular basis. These two don't go well together as you can imagine.

I live between various countries (none of them embargoed by the US, which AFAIK are the only ones excluded from Coinbase) but I have a US company and a passport with those shiny stamps that could clear any doubts about me sneaking through "El Hueco". I was not given a chance to show them however, so I'm just glad I don't use them regularly.

I'm sorry I don't have a great mistery story behind this :P