To summarize: people have known that cows’ methane production can be reduced with an appropriate diet for quite some years. There has been a fair bit of searching for what that diet could be - tropical algae from high seas may produce the right outcome but aren’t readily available where the cows graze.
It is nice to learn that daffodils also do the trick, and reduce methane production by “at least 30%” (a cautious estimate, some results using artificial cow stomachs have given a reduction of 96%).
I suspect the compound isn’t necessarily the same as in Asparagopsis taxiformis (one of the weeds that work), but the similarity is on another level of abstraction - it influences the gut microbiome in the same way, favouring certain bacterial species and metabolic paths over others (because bacteria often have a choice of “how to eat” - which chemical reactions to perform).
Can’t be sure with the limited information published, though.