When I was at a local radio club today, I witnessed a bit unusual response by a station calling CQ using BPSK31, that is to say phase-shift keying, not the regular A1A telegraphy, on the 20 meter band.
The communication looked something like this:
CQ CQ CQ DE XYZ1ABC CQ CQ CQ DE XYZ1ABC PSE K
XYZ1ABC DE ABC2XYZ KN -- our reply
ABC2XYZ DE XYZ1ABC SK SK -- their reply
After a minute or so of pause, the station called CQ again.
Rest of the guys at the club weren't sure what the other station meant by SK so we interpreted it as not being interested in a contact and moved on.
Objectively looking, the other station had no reason why not to be interested: Looking at the last few months of the log, there weren't any contacts with it. It wasn't calling DX or any specific territory and the distance was reasonably large, in the range of 3000 km.
So my question is: Is the interpretation of
SK as used here correct? Is there some standard response to such a reply?