I always thought it was just a variant of a dogleg (or maybe a reverse dogleg?). Case calls their whittler on a similar frame a "seahorse" (after its appearance when blades are open), GEC called their whittler a "Grinling" (after Grinling Gibbons, I assume). When used in different blade configurations, GEC gives it different names to distinguish it (38 special, Willamette, Farmer Fack, Orchard Gem, etc.). I could be wrong, but I think the general identifier of this frame is a dogleg. How a particular manufacture names a given variant is more an issue of marketing/identifier.
The OP asked about it being a "jack." Again, I could be wrong, but I think that "jack" is any knife whose blades are all located on the same end. Because of I this, I've always thought that single-bladed knives are
technically jacks (because "all" blades are, in fact, located at one end), but I usually think of two-bladed knives (with blades pivoting at the same end) as the quintessential "jack."
I'd call the #38 pictured by the OP a single-bladed dogleg (or maybe "reverse" dogleg???). But there are many here with much more knowledge than me.
At any rate, it's a great knife, OP. I love how red linen gets darker over time. You just love the knife more the more you use it.