I can't paste the pictures here, but if you look at both pitches in his descriptions, the grips are pretty much the same. The description for the straight curveball is basically the karate chop motion. Can't do that with the low 3/4 slot. With the slider, ball comes off the side of the index finger, which is more conducive to the above slot.
Just seems to me that if you tried to throw the straight curve from a low 3/4, it just wouldn't work right. Your hand would be under the ball.
I don't pretend to know it all. That's why I've asked the questions to start the thread. I just think it may be a matter of degree whether you are throwing a curve/slider/slurve from a low 3/4. Maybe it should just be called a sidearm curve rather than a slider??? Not sure.