Having worked in universities he has missed out a key underrepresented demographic, white men from underprivileged backgrounds. They are often the biggest demographic that don't receive the same opportunities (and there are official stats to prove that)
There are subjects and industries that don't receive a variety of applications in terms of demographic. That's not for the want of trying, unis actively outreach to schools and colleges etc to try and encourage wider demographics (especially girls) to be interested in engineering and technology subjects. Race wise they are open to all, with some subjects receiving higher applications from perceived minority backgrounds.
I think its more to do with cultural backgrounds, current pop culture of what's seen as trendy, and socio economic issues that stop people applying for certain things. And as for the industries themselves, do graduates stay in the country or do the work abroad, something common especially in engineering.
As usual with twitter, it is completely devoid of context.