Nothing about it has been said as a sequel, it's just set in the same world from the looks of it
. (which I guess you could consider it a sequel based on that alone)
But if it makes you feel any better, ReDigitize was not the first game, it itself was a sequel to Digimon World PS1 as ReDigitize is set sometime in the future after World 1 from what I read on it.
But honestly any Digimon games released overseas should be cause for celebration. It was all but dead until the CS announcement.
Gotta hope it sells well so Digimon games come out here in the future. New Order and whatever comes after that.