That much dust came off the radiator. The dust was heavily reducing the cooling of the cpu.
I can't stress this enough. Cooling systems full with dust reducing the cooling throughput your computer.
What do the Pictures “tell” you? The air flow isn't going through very well. If your computer is under high load, it could happen that the cpu or gpu are throttled. because of high temperature.
In worst case: When it's getting really hot, one of your computer components may overheat and causes your computer to get slower or just turn off.
TL;DR Keep your computer clean.
I personally clean my computer every 4 to 5 months and so should you too!
Have fun keeping your computer clean! :)
EDIT: I cleaned my computer again after I didn't do it longer than I want to admit.. Here is a video of the dust in the radiator:
Well.. I should clean my radiators on open case machines more often.