I think it's more of a "spiritual sequel."
It inherits a bit of game play and a frog theme, but isn't a true sequel. Frogger wasn't even Sega's game. They just released it. I guess by that logic, the "true" sequel to Frogger are the GameBoy Advance and PS2 games that Konami's released in the last couple years.
It seems everybody who's had the license to Frogger has wanted to make a sequel. First Parker Bros (Three Deep for 2600, etc), then Sega, then Hasbro (for PS1, DC, etc). At least Konami has the license back to their own game.