Could well be wrong on that though.
No not an incorrect statement at all, Dieseling is a fact, that any "petroleum / Oil" based product, Oil, Grease, will cause a very large increase in the speed the pellet leaves the weapon.
I have seen an Air Rifle undergo a [non Dieseled ] test and it was rated at 10.6 Foot pounds a few drops of [in this case 3 in 1 Oil was added to the breach, behind the Pellet the weapon tested and its power had moved upwards to [about] 17 Foot Pounds. i cannot recall if it was a 0.22 or 0.177?
Any air weapon over 12 Foot pounds will have to be registered and a Fire Arms Certificate obtained [if possible] bottom line is that if you are found with an air weapon that produces anything above 12 Foot Pounds that is a Firearms Offence, if you do not have it registered and hold an FAC, for the weapon.