Yes, the non-upgradability of RAM on MacBook Airs and later other MacBooks has been widely called out in reviews and media at the release of those models. You can easily verify that by going back to read those reviews.
That doesn't mean that it was the first, just the first that they bothered to look for that... which makes sense, because apple's hardware is generally going to be under more scrutiny than other manufacturers.
They were certanly the first to implement that and starters of the wider trend.