Looks like someone slipped it into 1st gear at 70 on the motorway.
I managed to put a Sierra Sapphire into 1st instead of 3rd at around 50/55mph ..... fortunately it was a hire car!
I did similar in a MkII Belmont, only it was nearer 70mph. And it was my car.
The father of a lass I was going out with in 1971 had a beautiful Jenson FF which he used to take up and down the A1 near Ripon at somewhat silly speeds... when someone pulled out in front of him when he was doing (so he says) a "mere 90", he manually stuffed it into a very low gear (it was an auto) .... where by there was a series of loud bangs and the engine died ... his words .... car was recovered to the dealers (which he owned) and was the cause of much looking and amazement ... there "appeared" to be hardly any damage at all ... except for 7 holes in the bonnet, and all 8 sparkplugs were absent !!
Cut a long story short .. the car was eventually written off as the engine/gearbox/both diffs and the whole drive train were beyond repair as each was examined ... and when they tried to fit new they would not mate .... it was eventually found the the whole body was "twisted" about 4 degress out of true !!
It was (somewhow) calculated that the engine had hit nearly 30,000 rpm, that the valves could not keep up, and that the pressure in the cylinders was sufficient to, eventually, blow the spark plug threads clean off, so the plugs left like bullets !!
The stress of all four wheels shoving that amount of energy "backwards" must have been amazing !! I was lucky .. he had let me drive it once, for an hour, the week before !! Amazing car for a 20 year old to drive !!