I'm not at all surprised that US sharing ISR data with Ukrainian is giving them a lot of success, I think that's plenty clear since early days of this war.
I am surprised by that statement the Americans made. It suggests they are worried about further Russian escalation? Against possible US assets?
According to Shilao there's an old man, an Ukrainian weapon expert in Beijing who came from Nikolaev who's been hitting the sauce hard in recent days following Moskva's sinking. He's very familiar with the Slava class and the last gig he did before leaving Ukraine for China was on the R-360 Neptune missile, so you can see why the news has hit him hard. Both PLA and North Korea military representative has been trying to get out of him information about the missile.
Neptune is based on Kh-35. Ukrainians purchased some clandestinely from Black Sea Fleet to further develop them into Neptune for export (hence the North Korean interest, they are also facing a certain 10,000 ton+ warship class). You have people like old man who knows both the original missile as well as old Soviet radar very well so they changed Neptune's seeker enough that it's tricky to defend against for old Soviet ships. Nevertheless it's not exactly bleeding edge ASM and if the Americans wanted Moskva sunk it seemed like they would have sent them something more advanced, so I'm not discounting that it may be true and the US was not directly involved.