If you ignore the plethora of open world series that have been around for years then sure. A handful of major series going in a more open direction does not make the statement that open world games only became a trend this generation of that it was really only GTA and skyrim before true. Nothing about your statement as you worded it is true.

If you don't believe me then feel free to see the following series that aren't GTA or skyrim:
-Assassins creed
-just cause
-batman Arkham city
-saints row
-yakuza
-fallout
-oblivion
-infamous
-prototype
-mercenaries
-Minecraft
-every Spiderman game since Spiderman 2
-every mmo ever
-red dead redemption
-red faction
-watch dogs

Im not even close to through all of the open world games and series from last generation but I'm getting tired of listing them and I've clearly made my point. Open world games aren't just becoming a big trend now. They've been a big trend for more than a decade now.

And if we're being honest, Zelda has always been open world. Not at the scale that breath of the wild was perhaps, but it's always had a big, open, non linear world to explore in all of those games.