The article mentions moisture several times, as well as draining moisture during the trip. It also explains liquefaction in terms of water acting on the solid, whereas I always thought it was just about granularity.

From the article, it doesn't sound like it's about trace amounts of water at all. It sounds like water is somehow involved in the loading process...?

The liquid is simply acting as a lubricant. So, it takes a very small amount to make a large difference. Really it's less soggy than simply damp.

So why do they mention draining?

Or large parts of SF during an earthquake.