Without some qualification, that statement is entirely pointless.there are just as many 'industrialists' billionaires on the remain camp.
Perhaps those millionaires and billionaires are content to remain in the UK and use this country as their tax base? I suspect they are perhaps less concerned with eternal personal wealth expansion than those who lobby for a tax regime kinder to the 5% while the plebs endure austerity.
Almost certainly, many of those remainers among the 5% will already have the vast majority of their fortunes squirrelled away in various tax havens in any case.
Tom