Subdimensional Quasivelocity?

Poul Anderson made a point of imagining a different means of faster than light travel every time he wrote a new story requiring this premise. (He had the scientific background to enable him to do this.) Thus:

he did not always invoke the sf cliche, "hyperspace;"

when he did use this phrase, he devised his own meaning for it.

His "hyperdrive" does not make a spaceship disappear into another kind of space where there is no light speed limit but makes many quantum jumps through ordinary space and thus has a pseudovelocity.

In earlier stories, means of FTL had not yet been worked out. In "Genius" (1948), "...quasivelocity..." (Call Me Joe, p. 197) sounds like hyperspatial pseudovelocity but is qualified as "subdimensional." What can that mean? The ship temporarily has zero dimensions in relation to the rest of the universe and thus is not limited to the light speed barrier because the latter applies only to objects that have a finite length and that therefore shrink in that length, although never reaching zero length, while they accelerate? Other dimensions are loosely thought of as other and higher realms, therefore "subdimensional" implies the lowest possible realm at which normal physical laws do not apply?

"Subdimensional" is probably an early piece of pseudo-scientific jargon without any rational thought behind it.