The only laptop I opened recently was a Dell and there is no way the dust I found inside could have been removed without opening the cover over the heatsink, taking out the heatsink and then blowing and brushing it.
I replaced it after cleaning the paste from it & CPU, and applied new paste before fitting.
It would be a surprise to me if there was no dust caught in the heatsink unless the PC is new.
That no dust emerged when blowing might indicate that no dust was disturbed, and not that no dust existed.
Just a thought ......