Difference between latches and flip flops in datasheet
When talking about the actual low level component, “flip flop” is generally used when referring to an edge-triggered entity and “latch” for a level-triggered one.
All the components in the HC595 are edge-triggered flip flops (as you correctly inferred from the truth table), so it looks like in the datasheet they are using the word “latch” in the lower components to describe the function, i.e. whereas the top flops are implementing a shift register the bottom ones are “latching” and holding the 8-bit value from the shifter.