The actual real life Formula 1 rules: "Pirelli nominate two mandatory sets for each car for the race (which can be of different compounds) and one further set of whichever is the softest compound that can only be used in the Q3 segment of qualifying, but the teams are free to choose the remaining 10 sets." "Unless wet or intermediate tyres are used during the race, all drivers must use at least two different specifications of dry-weather tyres in the race, at least one of which must be one of the two mandatory sets nominated by Pirelli, though the teams are free to decide which one."
Spanish Grand Prix tyre allocation: "They are the orange-marked hard compound, the white-marked medium and the yellow-marked soft. Under the new-for-2016 regulations, teams must have a set of hards and a set of mediums available for the race, and must use at least one of them."
There's nothing within the sporting regulations that says you can't qualify on the mandatory tyres, merely you have to use them in the race. So what Matt did was technically legal, but theoretically disadvantageous.
Put Matt and Ben in a McLaren or a Haas or something. Perhaps a Toro Rosso. The Sauber is hardly, if at all, any better than the Manor. And Scott should have cheat codes to make it even remotely fair.
Matt needs to use Hards because he Qualified on Mediums and was inside the Top 10 so they aren’t new tyres. Fernando Alonso Qualified outside the Top 10 so at the start of the race chose Mediums.
There's nothing within the sporting regulations that says you can't qualify on the mandatory tyres, merely you have to use them in the race. So what Matt did was technically legal, but theoretically disadvantageous.