Initially, Miele did focus only on road bicycles, as nearly as I can tell. Towards the end of the eighties (best guess) they entered the mountain bicycle arena. I have run across quite a few old Miele MTBs and found them all to be fairly well made. The picture supplied by the OP is not clear enough for me to make any kind of call on quality of the bicycle.

I should have scanned all the pictures from this Miele brochure - there were several mountain bicycles presented.