The first is a padded vest, the second is padded shoes.
Mushroom Vest (500 gp) This spongy, mottled brown vest is several inches thick and composed of woven strips of preserved fungus. The vest feels soft to the touch and springs back into shape no matter how badly compressed. [...] It protects you from impact trauma. When wearing the vest, you treat any fall as if it were 20 feet less when calculating damage.
Boots of the Cat (1000 gp) The boot’s wearer always takes the minimum possible damage from falls (as if the GM had rolled a 1 on each die of damage incurred by the fall) and at the end of a fall always lands on his feet.
RAW there's nothing saying you can't get benefits from both; while the boots specify you automatically land on them, the vest doesn't specify you have to land on it to benefit from it, but does that make any fluff sense? Would you allow it as GM? Perhaps only when the PC rolls out of the fall thus lands first on the feet and then on the vest?
Or could the vest simply be doing something completely magical to protect you from impact trauma? To me it seems the only thing magical about it is that it is incredibly good padding material and regains it's shape well. The last sentence here seems more to mechanically make use of that, based on the assumption that landing on a padded vest (since normally falling and taking damage always means you're landing prone) would hurt a lot less.