It didn't really look like a smart phone game
It's probably PC, Switch and PS4. It's probably being made for a different market than the MMORPG market that already owns X Online
It's definitely possible to render those graphics on smartphone... The part of the game that this is a remake of is about 10-15 hours at best to complete, and is free to play on all those platforms already, so I don't really see how they would have much success monetizing it on those platforms, and if it was purposely made so that it could be sold in Western markets, wouldn't it have been mentioned during broadcast?
Edit: this is just speculation, but I thought I should make it clear my point of view as someone who actively plays DQ10 and knows a bit about its current situation.