90 degrees is SOUTH, not NORTH. I noted this in my original comment that was removed. :p 270 is north.

It must be because in a normal graph, you'd have the positive values on top and the negative values on bottom, but on the screen the values are counted from top and towards the bottom, so it's inverted, kind of.

the v3 sin/cos stuff basically directly maps to libc sin/cos, so, it should function the same way. Since I used sin/cos extensively in timeless I can say for sure it goes clockwise. The bit about the orientation of the coordinate system seems like the most likely explanation for the seeming discrepancy.