I'm not sure which "IFAB rules on deliberate handball" you are reading, but the actual ones here have lots and lots of "wiggle room". There is a misconception about what is and isn't a yellow card for handball. It is very clearly a foul, but a handball is only a yellow card in these circumstances if it is done to "interfere with or stop a promising attack". That is by no means a straightforward and obvious definition.
For me the Bitton one doesn't fall into that category. If the ball gets through to McKay then he's in a wide area, about 50 yards from goal, facing his own goal and with loads of Celtic defenders goalside. For me a "promising attack" is something that will get fans starting to be out of their seats and expecting a chance of a goal, for example a 3 on 2 or something like that. You can basically think of it as "if he tripped him in that area of the park would you be expecting a yellow", because it's the exact same definition used for that.