Hmm weird, do you want to check whether that's still a problem with the current development version?
You can find it here (bottom left): http://www.openclonk.org/nightly-builds/

PS: is that really only in the tutorial? (I am not at home right now and cannot test whether I have the same problem)

The clonk always digs in the direction of your mouse cursor. In the video, the cursor appears to be in the upper left corner of the screen, therefore the clonks tries to dig upwards. The tutorial says

"Wähle die Schaufel aus und du kannst anfangen in die Richtung zu graben, in die du zeigst."

"die du zeigst" refers to the cursor position. It's not clear, so I'll go and change it into something more precise.