Said another way, most birds have the backwards-looking feet/legs. Because, like the flamingo, their upper leg bone / femur-equivalent is relatively short and mostly tucked up against the body. And their lower leg bone / tibia-equivalent is a little / a lot longer and more exposed.
The thing that makes flamingos really stand out, besides just that they are very long-legged for their body size, is that the upper foot bone and the lower leg bone are very close to the same length. And therefor look similar to human legs whose upper & lower bones are also about the same length.