You mean you changed the resolution of your internal screen with xrandr? Or does xrandr still report 3200x1800? If not, then this is not a HiDPI setup. HiDPI is (basically) when applications draw using internal coordinates that are not "1 screen pixel per logical pixel", but more than that.
No, I just changed the "Display settings" (right click on desktop) to 1920x1080.
xrandr reports the following:
Screen 0: minimum 320 x 200, current 3840 x 1080, maximum 8192 x 8192
eDP-1 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 294mm x 165mm