Honestly not 100% sure how it is currently calculated. From what I can see based on the UpdateCraftSkill function, it doesn't look quite right.
The chance for the player to skill up from crafting an item from a profession (not considering changes to configs) should be
((GraySkill - PlayerSkill) / (GraySkill - YellowSkill)).
Vanilla Wow wiki/Wowpedia (both of which cite a Wowhead comment), and an r/woweconomy post, likely got it from the same comment.
Windows 10 x64
@heyitsbench can you check it out.