Bob C Cue
Quintessential Chatty Farker
I think by vertical, Fwis is speaking of the meat spinning end over end, where several loins could be stacked side by side, rather than the loin being skewered from end to end along its axis. Not being a roti guy, yet, I don't know that a typical roti can accommodate a pork loin skewered the way that Fwis is showing here, let alone several in a row. Now, how that pork loin is actually being carried by the rod, and not just hanging in a stationary position while the rod spins inside it, is a question for Fwis to answer. Clearly, something is not being shown in the photo.
Maybe it's like those hotdog spinners you see at movie theaters and such places.