You said that the chairman's remarks pre-dated Trump's steel tariffs by approx two years, so just after the referendum.
The value of the pound had dropped. Steel prices had been rising before the referendum but actually dropped slightly in Q4 of 2016, before continuing to rise.
So no quantifiable Brexit effect on steel prices... you and your Remain buddies are in such a rush to blame Brexit for everything negative that happens you don't appear to even understand what you are writing.