Hello @Aurine, and welcome to the forum!
Can you please describe how you tried importing this bundle into your Krita? Did you try it this way, or did you try it via File > Open, which is the wrong way?
A bundle is installed in Krita via the menu ‘‘Settings’’ >> ‘‘Manage Resource Libraries…’’ and in the opening dialog you have to click the button + Import in the next dialog browse to the downloaded bundle, select it and confirm the selection. Now Krita imports that bundle, and you can use its content, so the brushes in case of this bundle.
In case this BUNDLE comes in an archive-file, like ZIP or RAR for instance, then you have to unpack the archive to get the BUNDLE-File it contains, then you can proceed as described above.
Michelist