I don't think it's a mistake. In one of the Killzone: Shadowfall trailers, the text is "VSA" instead of "ISA."
I'm assuming the ISA is no more. It's probably something like "Vektan Strategic Alliance" now, due to the Helghast and Vektans living together.
Dude, lol
Hopefully this (and Knack and DS4) are available when my sister is in Florida starting next week.