No he's saying if you're trying to write code in an edit box in a web browser (for example) and you press tab, instead of inserting a tab character it will move the focus to the next input field.

Bullshit reasoning though, because even people who use spaces for indentation don't do it by hammering the space bar - they also press the tab key. And of course in modern browsers we can give tab the expected behaviour.

The only logic I've ever heard for using spaces for indentation that actually makes sense and I vaguely agree with, is that lots of programmers do not give a shit about formatting code and even using spaces properly is often a bit too much for them.

That doesn't matter so much if you have an autoformatter though, so with the exception of Go I don't know why modern languages with widely used autoformatters don't use tabs.