That doesn't mean anything though. Plenty of games use old engines that are just built upon. In fact, most do when it's a long running series. 'New engines' are a rare thing.
I mean, sure, but using an engine built back in 2001/02 up until 2017 doesn't seem very common. Most of the times there does get to a point where they need to build a new engine with each turn of the generation. Square Enix tended to do this every generation change, for instance.
EDIT: Also, this could probably be chalked up to Sega being Sega, but Sonic had no consistency with any engine and except certain stretches on certain platforms, it often had an entirely new engine for each new game. Sonic Adventure 1 and 2 are different between games, Sonic Heroes, Shadow the Hedgehog, and Sonic Riders, are probably the most consistent in this regards, Sonic 06's engine was not reused (outside of bringing over Havoc) outside of that game, Sonic Unleashed and Sonic Generations do share the same Hedgehog engine, but the Wii games often had new engines (though I believe it was confirmed the Hedgehog engine was running on the platform, but they couldn't realistically do what they wanted). Then I believe the Wii U games were all different engines, and Sonic Forces was a new engine that, while can do modern effects, struggles to be able to load as much information like the previous Hedgehog engine.