The bikes look a cross between 90's MTB's and Cycle-Cross bikes. Tyres that are 37mm+, drop bars and rigid frames. The bars on most bikes are splayed to increase control and comfort.

So why a gravel / MTB Adventure?  The route would suit both bikes and riders, not MTB associated with huge down hills ar big jumps and technical sections, just long distance, good old cross country - Old Skool.

Gravel fills this gap perfectly, not road but ok on road, not MTB but ok off road, a real adventure bike.