It's ironic in the same way that adding the text "DEFACING STOP SIGNS" under the main text of a stop sign is ironic.

The method used is the very one which is being condemned / warned against, and the fact that it works better than other methods (in both examples) only adds to the irony, as one should assume that something that preaches not doing exactly what it's doing would invalidate itself, rather than its actual effect of producing greater results due to a quirk of humans.