I would think that damage to primaries is fairly likely in a captive bird, if it flies against the bars of a cage - probably at least as likely as damage to the rectrices (but harder to see in the field). It is also extremely rare in wild birds - while I agree that we are looking particularly closely at this bird, we do also look at other birds (especially when bird ringing) and do not see this sort of damage.
I would also like to point out this picture:
http://www.hkbws.org.hk/BBS/view ... &extra=page%3D1 (possibly the only one showing the wing fully extended?) which to my eye seems to suggest that the damage is not restricted to a single primary, but also to other adjacent primaries on the left wing (is the tip missing on the 3rd primary?) and possibly other feathers (there seems to be a gap in the secondaries on the right wing).
I think the most likely explanation for this bird is that the damage has resulted from a period in captivity, rather than the coincidence that a potential first record involves a bird that also shows abnormal plumage damage.
