Nope, you’re coworker is right. That is, assuming that coffee grounds act like all other plant matter in the world that I’ve ever tinctured by the percolation* method. Thicker or layered cloth or harder packed marc (plant stuff) slows down the percolation, or the “drip”, which means the solvent (water) has prolonged contact with the marc, and extracts more constituents from it.
In the case of coffee, this means not only “stronger” as most of us think of it, but more bitter, as the bitter alkaloids take longer to dissolve. A regular packed coffee maker is carefully calibrated to remove just the right amount of bitter - slow down the process and it gets too bitter for most people’s taste.
*The percolation method of tincture making doesn’t mean the same thing as percolating coffee. Rather, it means packing plant matter into a cone of paper (often we use coffee filters for this) and pouring water/alcohol on top of it and letting it slowly drip through over a period of roughly 24-48 hours. The resulting liquid is as chemically strong as a traditionally prepared tincture involving simply soaking the herb in the same mixture for a month. The movement of the solvent through the herb speeds up the process considerably.