My original comment was regarding BOATs in the UK (and chemins in France) If the road/track they took in Spain was a legal 'route' like a BOAT...it is irrelevent whether there is a 'better route to travel'. I presume you live in Spain...what is the legal status of the myriad of dirt tracks that locals drive and ride motorbikes on? (Genuine question...not after an argument or internet oneupmanship)
Some of the tracks in Spain (pistas) are classed as dirt roads. The ones through the "Badlands of Gorafe" I don't know. I do know that we had to be very careful riding some of them on our full suspension emtbs, and avoid the water washed channels, and we needed full boost to climb up some of the very steep hills.
We've taken our motorhomes off road many times, as participants in Spanish Orienteering competitions, and having to drive to the parking areas, but we wouldn't choose to drive some of the tracks we've seen some people attempting.