Difference OpenFietsmap/OpenStreetmap

What is, may be the “gross” difference between the two?
And: in the map of Openfietsmap for Garmin (W3) I find sometimes blue dotted lines, sometimes nothing on the same road, and or red dotted lines?
Are these bikeroads per sé? (why the omissions?)

OpenFietsMap is based off OSM and is designed for cyclists. So cycleways are highlighted (the dotted lines) and the routing is tweaked so that the gps device picks the most cycle friendly route.