Obviously I have no idea who voiced Smirkenorff at the time. They hid that kind of stuff from us.
However there is a related oddity in this room. Dunstan insisted on telling this particular joke and whomever voiced Skirkenorff didn’t know the format. In the original take, Smirkenorff burst out laughing as soon as Dunstan said “to get his pension”. Right at the end of our quest they brought Paul Valentine back in to rerecord the audio and tell the joke properly. If you listen very carefully, you can tell the audio changes.
So it could be some kind of weird audio matching going on.
The only other point of relevance is that to establish this shot, the puppet would need to be in the adjoining void (together with Clifford). It may be they were trying something to make the audio a bit less irritating for the dungeoneer (who would inevitably hear the audio twice).