I'd guess the commenter means, that from a Marxist perspective, most workers are not 'capitalists,' i.e., they don't make their living from owning capital. These 'non-capitalist' workers get wages primarily from capitalists. Perhaps the author is moderately successful and does live off of investments now. That could technically make him a 'capitalist' - again, from a certain perspective.

I'll readily admit this is mostly a semantic difference, but to me it serves as a good reminder that, for example, calling even the most ardent free market supporter minimum wage WalMart worker a 'capitalist' is about as sick of a joke as pretending that the majority of jobs offers workers a chance of building 'capital' in the first place - as the author points out.

Even if Patrick is or has been a CEO of some sort (I don't know anything about him past what I've read today, but another commenter mentioned that he's working at Stripe), the fact that most of the article talks about how to make yourself more marketable to employers (by building up a capital of sorts, as he calls it) indicates that he has spent a good portion of his life selling his labor for wages. Something that people who own real capital (i.e. lots of money, infrastructure, the means of production, etc), i.e. capitalists, generally don't bother doing.