Where on earth were you hearing about SPAs and server-side JavaScript in 2004? Was "SPA" even a term before about 2010?
It used to be called Ria,"rich internet applications".Then ajax apps before...nothing new here.
Probably he doesn't mean only JavaScript SPAs. The term was introduced around 2010, but the concept is older. Flex is from ~2004 and is typically used for SPAs which behave like the modern JavaScript applications - they just target the Flash platform instead.
tl;dr Wake me up when even 5% of sites are SPA.