Well it is still going to get dusty inside the case as hes pulling dust/air in for his radiators.

What if they have filters?

The fans would be placed on the radiators (no room for a filter) any addition of a filter in a computer chassis or on a radiator would drastically reduce airflow. He's using multiple small fans (presumably to increase airflow while minimizing noise/vibration) instead of a large 120mm+ fan.

In the picture attached you can see he is not using a filter (I didn't expect you to research his setup this is just simple pointless commentary)

This system actually uses liquid cooling (that's what the green in the pipes are)

What a lot of people don't realize is that liquid cooling still requires fans in 99% of situations (common mistake).

The commonly agreed "best" liquid cooling setup is a push/pull setup (shown below)
A heatsink is applied over the top of a heat producing component (CPU, GPU, etc) This heatsink has cool fluid running into it with hot fluid running out. The hot fluid flows towards a radiator which air from the push fan flows through and its pulled out by the pull fan in order to remove the heat from the liquid. After the liquid transfers heat to the radiator it returns to the heat sink as cool fluid to repeat the cycle.

It's similar to the design of a car radiator.

Awesome! That was really informative, thanks:)

No problem.