Derek, I’d the same objection on first glance, but what happens (well, one can take this
perspecitve, anyway) is that the interlocked loop’s lower-right edge is pulled in that
direction under the opposite rope for the end-tuck, and in so doing, the other end
swings towards a diagonal upper-left orientation, and gives the un-interlocked look!
Or, to put it another way, were they indeed not interlocking, you’d have to specify the
tuck of the end pointing up&leftwards.
The simpler knot that is presented following the first is what Harry Asher named
“Corrick”, and is #1451 in ABOK (“Ashley”). --doesn’t look strong to me
(or to Ashley), as the SParts come to a hard u-turn against each other.