Lots of people had doubts when it was announced whether it's real or not. i think it's just a PR move.
REASONS:
1. Both had dating news already. Jennie with kai and Gdragon with some Japanese model or someone. So it was not really a surprising news and the reception was lukewarm too.
2. The biggest reason to not believe is that according to rumors that somebody posted on a allkpop dating tea thread; another member of blackpink was dating someone in 2019 and maybe early 2020 which would have been a bigger news especially in 2021. At first it sounded like made up rumor because it was so unexpected but some of their other rumors seemed true and i watched some fancams where she visibly seemed sad or acting annoyed when she sees him.
3. The reason for PR is that bigbang were a popular group but inactive since 5 or 6 years and had serious scandals. YG plan was to have them perform in coachella to show that they still are in demand as ever but that got cancelled due to covid. So now they keep them in news with fake pr news and they will have comeback this year or maybe gdragon alone. Regaining them their popularity will also help in them promoting their junior groups Treasure and another new boy group that YG is already preparing.
If it was really PR then it didn't work because 
