The Time Lab might have come out of a portal, as has sometimes been suggested, but from the text and who is speaking, it seems reasonable to propose that Belthasar appeared in 2300 AD and created the Time Lab. It would be like in the modern world if suddenly some unknown scientist at some unknown lab started publishing revolutionary research. One might say that they came out of nowhere (or out of left field, if that gives a better idea of what I am getting at).
The speaker doesn't know that Belthasar traveled through a gate, so we must keep in mind that he wouldn't have know that a lab may or may not have traveled through a gate as well.
