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

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.