The ad in question appeared in UK television back on October 23, 2017, and was taken to task because it failed to make it clear whether or not an Internet connection was required to access content found within Gran Turismo Sport.
More specifically, the ad demonstrated gameplay that featured both a variety of tracks and cars that all weren't available on disc for players to use offline. In other words, it was showing content that was only accessible if you had an online connection, whilst not making it clear said connection was needed for said content.
"The complainant challenged whether the ad was misleading because it did not make clear that an Internet connection and subscription to the PlayStation Network were required to play the game," said the ASA in a statement.
Sony responded saying the opposite that an Internet connection is not needed to play the game, and that while the exact track shown in the ad requires an Internet connection, similar tracks offered for the same experience are offered. Presumably, what Sony is getting at is that it's not misleading because there is substitute content that is available offline.
Sony continued by noting more that 75 percent of PlayStation console owners in the UK have been connected to the Internet at some point during the course of October when the game released.
Despite Sony's counter-claims, the ASA concluded that "the majority of the game was not available on the disc" and required an Internet connection to access. And Thus the ASA ruled to uphold the claim, saying:
"We considered that the requirement of an internet connection was material information that should have been included in the ad and therefore concluded that the ad was in breach of the Code."
Gran Turismo Sport, developed by Polyphony Digital and published by Sony Interactive Enertainment, is available for PlayStation 4 exclusively, where it has been since its launch back in Octobre 2017. It is notably the 13th game in the iconic racing-sim series, and the first one to hit the PS4.