Ideally, you use the same or similar material for the substructure and joints... Why... The sand simply trickles through with a gravel bed... You can often refill it, if you don't do it, you just have completely empty joints... With all the disadvantages
That is not entirely true. When done professionally, nothing trickles through. I actually have both on my property. Stones on a sand bed with sand in the joints and the same stones on a gravel bed with sand in the joints.
In fact, I have more problems with the terrace (sand bed and sand joints) than with the other construction. The stones on the gravel bed still look freshly laid after years, and the joints have rather increased than decreased.
With the sand bed and sand joints, on the other hand, there is always something to repair.
So in my opinion, everything was done correctly here by jucre45. Except for the missing (possibly insufficient) drainage.