The Heroku status site is indeed hosted outside of both the Heroku platform and EC2. It has been that way for at least a couple of years that I have direct knowledge of, and probably longer.

The page wasn't available earlier so something from their stack is probably shared. Maybe the problem was is in how they route the traffic to this status page. Bottom line, this page should stay up and the only way to almost guaranty that is to make sure nothing is shared between heroku's infrastructure and where/how the status page is hosted/served.

It's entirely possible that the status site had an unrelated issue. It happens. That said, I ran their stack until 2 weeks ago, so I can speak authoritatively on this: Nothing from their stack is shared with the status site. Period.

If that's the case (I trust your authority in this), then maybe the status page went down because of the spike in traffic.