That can be true when the problem is that the transaction fees are high, but sometimes (particularly when there's a slow block) they're unstable. So you might place a 6 sat/byte transaction fee on your transaction with the expectation of a 90% chance of "within the next block", but the next block comes out 35 minutes later and it's stuffed full of 10 sat/byte transactions. So you end up bumping the fee with CPFP and the transaction takes an hour for the first confirmation instead of 10 minutes.
But I wasn't talking about that. I was talking about the even rarer cases when no blocks get mined for an hour or more.
They're probably just referring to the (historically decreasing) variance in time between blocks, nominally 10 minutes. Not an outage by any stretch but occasionally annoying. It's smoother in higher frequency blockchains.
Previously: https://news.ycombinator.com/item?id=30346082