LDO maximum output current during short circuit
1) You already found the max short circuit current. The footnote in the datasheet clearly says that negative currents mean current out from the chip.

2) It may be limited for safety and heat dissipation reasons so that during short circuit the regulator does not overheat and get damaged, but also so that the short circuit external to the chip does not melt wires or anything. So basically it may not need extra short circuit protection. How the chip does the limit internally is not mentioned in the datasheet, it is not important how it does it. It can use many ways depending on the regulator topology.