We always had over the air (OTA) Zigbee firmware updates, but only for device manufacturers who sent those updates to SmartThings, of which there are not very many. (And IKEA is not one.) we still don’t have third-party Zwave updates.
What you probably saw was a new feature which causes Zigbee devices which have a firmware update available to show up in the SmartThings app with a little blue U-turn arrow on them. It’s the icon that’s new, not the functionality.