Buzzed?

So I'm flying IFR down V441 in Florida today, when I hear the
controller who's working me call traffic to a VFR airplane he's
providing with advisories. "Traffic, twelve o'clock, opposite
direction, very fast, same altitude, suggest you descend now." The 172
he's talking to descends in a hurry, and the traffic passes without
being seen. A few minute later, the controller says the same traffic
has circled around and is now coming back at the VFR airplane once
again. Once again, negative contact. Next time, the traffic is reported
circling ahead of the 172, until he breaks off and again makes a pass
around the Cessna. This time the now rather panicked VFR pilot see the
traffic, and reports it to the controller as "some sort of single." The
controller points out that at 250 kts at 5000 ft, it's unlikely to be a
piston and it must be some sort of jet. The pilot then asks, nervously,
if the building he's flying over is a nuclear power plant, fearing, no
doubt, that he's been intercepted. Negative, the controller replies,
and still no-one knows what's going on. At this point, I have to leave
the freq for the next controller and so I miss the ending, but I wonder
if this was indeed an interception, but if so, wouldn't the controller
know? Coincidentally, or not, a small plane crashed into the terminal
at Gainesville just south of there around that time, so perhaps
"someone" felt there might be rogue airplanes out there? Comments???