I can see a couple of things wrong with this "histogram". First, the vertical scale is marked 0 / 25 / 30 / 35 etc. On a linear scale, the first value should be 20 not 0 (or 0 is correct and the rest of it is wrong). Second, if we ignore the vertical scale markings and just think of the vertical scale graduated in "small squares", it looks as though frequency (not frequency density) has been plotted, with one unit of frequency mapped to one square vertically.