This doesn't say that expenses in retirement are higher than during your working phase (though they can be, especially if you travel a lot during the first few years).

What this is saying is that out of your retirement budget, housing is the largest expense, and the one responsible for the overwhelming portion of year-over-year spending increases.

For example, you could be spending $100k pre-retirement. Then, in retirement that could drop to say $80k. Of that $80k, housing may account for $30k, or 38%.

In a later year, you might have to replace a roof, so your housing spending goes up to say $36k, and your overall spending goes up to say $90k (because you also went on a somewhat expensive trip. The housing-related increase of $6k is 60% of your overll $10k increase.