I was going to tell you to google on “vacuum energy” but when I did that the first links to come up were an amazing set of garbage.
Here’s the Wikipedia page on vacuum energy.
The first thing you see is that “empty” space is not, in our understanding of the quantum world, really empty. Nothing is or can be.
The quantum world is totally probabilistic, and our best understanding of is says that that implies that the underlying reality is as purely random as anything possibly can be. Therefore the appearance of particle pairs (or the universe) is a truly random fluctuation. So that implies no cause, just one spontaneous randomness that happens to have larger consequences.
However, current physics can’t say anything meaningful about the instant of beginning of the universe. It is assumed to be spontaneous, but cannot currently be proven to be so.
Note that your link states specifically that its argument is a scenario, possible but unproven. I don’t think his argument is a good one on philosophical grounds - it’s basically as much hand-waving as physics. I think I agree with the conclusion regardless.
Your problem in understanding the piece is that you walked in on the middle of an argument. Everybody is making assumptions about what is known and understood. Even when nothing is.