The point still stands outside of Javascript, though. Unless you're dealing with very large databases, retrieving a boolean or doing a null check on a timestamp are pretty close operations, especially if you use some kind of frontend to render the data.

Storing a boolean expression ("is published", "marked as read", etc.) as a timestamp can still be valuable. It just happens to be entirely equivalent in Javascript, but in normal, typed languages, the same practice can be used to prepare yourself for debugging a broken application or database later.

I don't think this is a practice that you should just universally apply everywhere, but it's worth considering in a lot of cases where people generally tend to use booleans.