Yes it's true. You can book a fare with a fare basis beginning with Fxxx or Jxxx but your booking code is something other than F or J and thereby reducing your chances of 'normal' points accumulation.

Many airlines started this trend long ago in Asia. CX for example, offers 'special' unpublished business class fares but all with "I" booking codes even though the fare basis will state J. Finnair also uses booking code "I" and none of these earn tier points on BA. You do earn miles though.

So the chances are very high that BA is following this scheme of things for their 50% off fares from HKG - still very very expensive when compared to similar offerings from other asian cities like BKK.