>>this also raises some questions
>>vis a vis whether in a world with magic the idea of a magical being
>>who delivers presents everywhere is credible or if it's fact.
>
>... I mean can we really call the concept of Santa "credible" in THIS
>world?
>

I dunno about this specific dimensional offset, but I recall in Symphony 1, Saionji mysteriously acquired a sword from someone matching that description. Combined with other mythoi, one might have reasonable cause to suspect one Odin Winterbeard as taking on the role for his own mysterious purposes, or possibly any of the other gods and goddesses who have been shown to be real, or at least reality-based.

So yes, within this overall multiverse, there is circumstantial evidence that the concept is at least -plausible- ;-)