Theyre all types of beans. I guess if you solve everything in advance then red herrings that 100% make sense and could be correct answers make sense, but the game isn't designed as if it's only correct to play by finding everything everything first, so it doesn't feel like I'm doing anything wrong by selecting a correct answer and submitting it to take it off the board

https://en.wikipedia.org/wiki/Kidney_bean
https://en.wikipedia.org/wiki/Lima_bean
https://en.wikipedia.org/wiki/Pinto_bean
https://en.wikipedia.org/wiki/Navy_bean

Edit: if the red herring overlaps with every group like here so you don't have to find everything to know it's the red herring, that at least makes it feel a bit less unfair. I still don't really feel like I'm playing the game wrong by submitting a clear connection though. I guess the designers disagree.