To be fair, if that poll is real he is polling shockingly well for a right wing nut job in a Democratic primary against an incumbent president.
Even if that were to be true, the only thing shown is that RFK Jr has no chance in the primary. Though, I am not convinced that is true when in 2012, an incarcerated inmate won 40% of the primary vote in WV against Obama. https://abcnews.go.com/blogs/politics/2012/05/prison-inmate-wins-more-than-40-of-democratic-vote-over-president-obama-in-wv-primary
With his ideas and policies, RFK Jr might actually poll above Death Santis if he attaches R next to his name.
Most of the Republican voters won’t even realize this is RFK Jr. and not their lord and messiah JFK Jr.
Problem is if he is polling this well he could run independently and be a spoiler.
I wouldn’t put it past him to try to run as an independent. Even though many states have sore loser laws to prevent failed major party candidates from launching an independent bid, I imagine he could find a way to weasel around that. The other possibility that I see him pursuing is getting attached as a VP candidate to a Trump ticket. RFK Jr has already stated that he would be willing to accept a position in a Republican administration, and has been flattered by compliments from Trump.