Yes, it could be another molluscum--they often appear in the vicinity after treatment and need to be mopped up with another session or two. At times it's hard to appreciate the "dimple" on these until they're frozen with liquid nitrogen. HPV tends to be on the shaft, rather than the base of the penis. Vinegar is unreliable as a test.
I'm betting on either molluscum or perhaps just a pimple. See the dermatologist as planned, and check it out.
Best.
Dr. Rockoff