Then you need to read the rule book.

The rule is that if ANY part of the body (other than the foot) hits in-bounds before any other part of the body touches out of bounds, it is a catch.

Watch the video closely. The foot hits inbounds (but only one foot, so that doesn't count yet). But then, watch what happens. The way his foot, ankle, and lower leg kind of roll to the ground, you can CLEARLY see that the shin touches inbounds BEFORE the knee hitting out of bounds.

It is a catch.