Hi, from what I know cycleways are considered more for "urban" cycling infrastructure and having cycleways in the middle of a forest would be misleading. Also I've seen that some of them have hiking difficulty scale tags which tell that those are used by hikers as well.

When it comes to safety, if there are actual physical sign that restrict movement of people or designate the use for bikes this can be added using access tags: bike=*, foot=*
But ultimately it is a responsibility of the trail maintainer to place appropriate warning sign so visitors don't come into danger.

https://wiki.openstreetmap.org/wiki/Mountain_biking

On a side note, are those actually official MTB trails endorsed by the landowner? It somehow seems to me that those biking features were built on top of existing hiking trails.

Cheers