Okay, I've looked at it, and the logic seems to be "if the Slider can 'dangle' from the ceiling, he will keep going in the direction he was facing while sliding; if not, he will turn around".
So the question the player would have to ask themselves is: "Is this gap high enough so that the Slider could transition into a Shimmier?"
In this case, the answer is no, because the Shimmier would turn into a Walker right away, due to his feet touching the ground. Therefore, one could argue the Slider's feet touch the ground immediately as well, as soon as he reaches the bottom of his slide. Therefore, he turns around even though there is a small gap he could walk into.
Therefore, I'm fine with the current behaviour, too.