Up here, I would call it out and explain that aside from differing metals involved, a lot of insurance companies wont insure a house with galvanized plumbing fittings. Like K&T and Aluminum wiring, they want assurances (in writing) that the home owner will update the plumbing.
As Chris, I would have explained it verbally and written it into the report as a maintenance item that should be monitored. It would not have been raised to a major concern (ie. summary) unless it was also showing signs of leaking.
Sorry I call dissimilar metals with no dielectric unions all the time don’t care if it is leaking or not its going to leak. Write everything and let the buyer and seller sort out what is important if its on the report no one can call out I missed it. Not up to me to sort out what is important.
Is the Male adapter brass or plastic. Unless there is some pure copper in that line somewhere I disagree with the need for a dialectric union. Brass valves in galv. lines last 50+ years. The rust looks to me like it is external (caused by moisture in the environment). The galv. nipple between the valve and the galv. fitting will normally be the first thing to fail.