Hi James, if anything that cable housing looks too long! Cruzbike recommends about 25cm in the instructions. The housing shouldn't have to contact anything at either end, it will be held in place where it bends around the bottom bracket.
Here is mine for comparison. I used a thin sheath rather than a full housing, but you should see the black sheath extending a short distance above and below the bottom bracket, and that most of the cable is bare:
Not the most important detail in the world, but there really is no need for a longer cable housing, or zip ties.
See also the PDF that Gromit linked to above, although those pictures are a bit out of date.