Yeah, and that listing has been up for nearly a couple of years now. It has a non-trivial language requirement - N3 Japanese isn't super high but it's also probably at least a solid year's worth of study for anyone who doesn't have it already, maybe more.
There's the same listing in the Japanese pages for native Japanese speakers. There are also job listings for pretty much every other job you could imagine at Polyphony. Either they're looking to hire for every single position in the company, or they just have ads up so that they can see what sort of applications they get.
It doesn't mean that they're looking to develop post-launch specifically, the recruitment has been up far too long for that to be the plan. They would have had to hire and onboard someone a while ago. It just means that they're aware that their AI team isn't where it should be. Which is kinda duh, but on the other hand at least they're self aware I suppose.
www.polyphony.co.jp
This is the guy who has been working on the AI for the last 15 years or so. Again, he seems self-aware that the GT AI is not where it needs to be. It's a little disappointing that a game of Gran Turismo's size and reputation isn't just going out and headhunting someone with known experience in the field, because that's what it probably needs at this point.