No, the same note is there for regular Hills on the Chapter B terrain chart. Plus, the rules themselves are clear, even if the chart seems overly clear. The rules trump the chart.
It may look like unnecessary redundancy, but the note also clarifies that TEM of DOT is not always true for Steep Hills -- so that the Korean Terrain chart is completely accurate. Otherwise, somebody else would point to the chart and say -- 'well, look, apparently HA is not applicable to Steep Hills because it says only DOT on the chart for TEM -- unlike the Chapter B chart.'
So, they are just covering all the bases. Not only that, for units to get HA from any sort of fire height on Steep Hills, the HA rules themselves would have to be exceptionally changed. This is not the case.