Saw neuro after visual disturbance, probable migraine. MRI to r/o mass, found 3mm hyperintensity ant. Parietal subcortical. Ref'd to MS specialist?

Depends. There are many lesions that appear on imaging as non-specific and can be seen in many lesions. There are exact criteria that are present which makes MRI useful in the diagnosis, discussing with another specialist might discern or eliminate this diagnosis. The finding on MRI is more consistent with migraine.
Rule out MS. Small MRI changes like these are rarely due to MS. They are more often related to head injuries, high blood pressure, smoking, or migraine headaches. Being referred to an MS specialist may be overkill. In case they know something more though, you can't fault their advice. It's not likely MS will be the diagnosis based on this information. At most, you may be asked to repeat the MRI sometime.
Unlikely to be MS. Suspect your visual disturbance and migraine was totally unrelated to the lesion seen on the MRI film, and would emphasize that one lesion is NOT consistent with clinically definite MS at this point. Would wonder about a coincidental finding of a vascular anomaly instead. If MS is consideration due to additional neurological issues, would obtain neck MRI also.