Per the FAAO 7110.65 Controllers shall issue traffic advisories(emphasis mine):
"2-1-21- Unless an aircraft is operating within Class A airspace or omission is requested by the pilot, issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima. Where no separation minima applies, such as for VFR aircraft outside of Class B/Class C airspace, or a TRSA, issue traffic advisories to those aircraft on your frequency when in your judgment their proximity warrants it. Provide this service as follows:..."
It then goes on to tell them how to give an advisory, that they should give you vectors to avoid if asked and tell you when the traffic is no longer a factor if you do not have it in sight. Sounds to me like the controller was spot on in this case. The aircraft may or may not have VMC, hopefully he was, but either controllers can't know one way or another. At least he was at a VFR altitude.
Yup. It's 2-1-21 6. that talks about the "...if asked..." you mentioned.
6. When requested by the pilot, issue radar vectors to assist in avoiding the traffic, provided the aircraft to be vectored is within your area of jurisdiction or coordination has been effected with the sector/facility in whose area the aircraft is operating.
More on this in 5-1-8
5−1−8. MERGING TARGET PROCEDURES
a. Except while they are established in a holding pattern, apply merging target procedures to all radar identified:
1. Aircraft at 10,000 feet and above.
2. Turbojet aircraft regardless of altitude.
3. Presidential aircraft regardless of altitude.
b. Issue traffic information to those aircraft listed in subpara a. whose targets appear likely to merge unless the aircraft are separated by more than the appropriate vertical separation minima.
c. When both aircraft in subpara b are in RVSM airspace, and vertically separated by 1,000 feet, if either pilot reports they are unable to maintain RVSM due to turbulence or mountain wave, vector either aircraft to avoid merging with the target of the other aircraft.
d.
If the pilot requests, vector his/her aircraft to avoid merging with the target of previously issued traffic.
e. If unable to provide vector service, inform the pilot.
