The chart shows safety altitude north of DIXIR as 7100. The clearance given descent according to procedure. No matter from where you come to DIXIR procedure doesn't permit descent below 7500 before DIXIR
First off, it's FL75 and not 7500 ft that's the level restriction. Second, why does FL75 apply at DIXIR and not FL90, that's the charted level if you come via the DME-arc?
Having FL restrictions rather than altitudes implies, at least to me, that this got to do with airspace and not terrain, even though terrain is quite high to the north. I am sure even southern Spain experiences significact low pressure areas over the course of a year.
There is no way the given charts and ATC clearance (as given) can be used to obtain a universal understanding among pilots. Crap charts and crap ATC instruction.