Removing everything but points using mkgmap style

I’ve compiled two mapsets for my garmin using OSM data and mkgmap - one with just POIs (no streets), which I have as the lower draw priority, and the other one with streets, but no POIs, which I have on top, to display.
The reason I have POIs on the ‘hidden’ one but not on the top one, is that I want to be able to route to them, but I don’t want to see them as in city centres they get clustered and the screen looks far too busy.

The only reason I don’t have streets in the bottom one is that they just aren’t needed, so might as well make a smaller file. Pleasingly, it is able to get the lat long of the POI from the bottom map, and then route to it using the top map’s streets. Curiously, it actually does display a POI using its icon on the bottom map when I’ve selected it. I wasn’t predicting this behaviour but I actually quite like it.

However, when I open the ‘bottom’ map in gpsmapedit, it hasn’t got any streets, but it has got polygons, like forests and lakes and things. This is even though the ‘polygons’ file in its style is blank, just like the ‘lines’ file.
Am I right in thinking that if it never encounters a type code for a particular element in the style, then it won’t make it into the output map at all? If so, why are the polygons still getting through?
Doesn’t really matter, but would just like to understand it.

Maybe in the info file it copies some landuses to your polygons file?