Based on everything I've read so far, it seems to be a "whatever."

[Koushiro's welcome message sure had been useful]

The gates between this world and ours opened as a result of the worlds merging, and that's how we came here.

From Izumi-kun's explanation, an "Evil Digimon" is most likely the cause of this merging. So ultimately, that creature is responsible for us being here. [a beat] Even if us being here is only an unforeseen side effect of its actions.