Was the traffic being passed to the IFR on his departure report? If so, it should have had a location and outbound track in the report. If you monitor the frequency you will hear all this information, you can then make an assessment of whether you are that traffic. If it's a random traffic report and you hear it:
'Centre, ABC, VFR, 10 miles south of xxx tracking east, A055'
'ABC, Centre, sqwark ident'
I have no idea if it was a departure report, but I didn't hear it. I suspect I hear only the ATC side of the conversation, i.e. the aircraft is too far away to hear. I also have no idea what area ATC is covering with combined frequencies. Do ATC want a reply from every VFR aircraft at 5500 within their coverage area? My assumption is no, but I'm happy to be corrected.