Just because Crystal Palace can win against Liverpool does not mean that they are improving.
Sometimes teams have their own plans, and luck also plays a role. I think Liverpool played their best, but it wasn't their best performance. If they had played seriously, I'm sure they could have scored more. We can see how the final results each season in the EPL haven't been as impressive as Crystal Palace performance, but Liverpool have always been far better. So, I can probably attribute Crystal Palace victory to luck.