About the true meaming of E = MC^2 I dont think he said neither something wrong nor rivolutionary
On the contrary , in my opinion, many people misunderstood the real meaning of the equation
Mr Thornhill claimed that mass and energy are property of matter
This is, at least, what I understood myself when I studied this stuff at school

The common mistake is the to assume that mass is a synonimous with matter
and consequently to assume that in a nuclear reaction matter is annihilated and turned into pure energy

The confusion matter == mass is due to the fact that mass had been supposed to be a constant for hundred years
Same as, before Newton, weight was supposed to be a constant and consequently a synonimous with matter,too

The claim :

The mass of photons is null

It is not complete, you must add

The mass of photons is null, at rest

A photon in motion has a momentum
It can collides with electrons same as it were normal material particle
In conclusion, quite often you read


Matter is frozen energy

Right, but also

Energy is diffused matter