Diesel engines require a very different fuel from spark ignition engines!
Petrol / gasoline fuel requires a high resistance to knock, hence the 100/130 performance number (or octane rating).
A diesel, on the other hand, requires a high cetane number, which is the ability to ignite and burn rapidly by heat of compression alone. The two requirements are opposite extremes and are incompatible. Road vehicle Diesel fuel (DERV) therefore has an octane equivalent of about 20! I haven't seen a figure for AVTUR but it is presumably very similar.
Putting diesel fuel in a petrol engine will cause severe detonation / knocking and a major loss of power. This may lead to rapid piston failure.
Putting AVGAS in a diesel engine may result in delayed combustion, such that the mixture is still burning when the exhaust valves open. This causes them to rapidly overheat, as well as a loss of power. Bye bye exhaust valves.
Also, a diesel engine relies on a high pressure fuel pump, operating at 3,000 psi or more. It needs lubricity in the fuel, diesel fuel has this property. AVGAS doesn't. Bye bye fuel pump.
This pilot should think himself lucky he's not being prosecuted for endangering the aircraft.
