Other people have answered more thoroughly, but it should be added that even your source never calls grass fed beef carbon neutral (on the very first paragraph it even says that it isn’t), just that it has a better CO2 footprint than grain fed beef (and that not by much, as has been pointed out)
I don’t have access to my schools library atm. But here’s one I found off google (which is admittedly a poor method to find studies)
https://smallfarms.oregonstate.edu/new-study-finds-grass-fed-beef-reduces-carbon-footprint
Full disclaimer I should have clarified in my original comment. Grass fed livestock specifically is carbon neutral
Are the majority of livestock grass fed?
Other people have answered more thoroughly, but it should be added that even your source never calls grass fed beef carbon neutral (on the very first paragraph it even says that it isn’t), just that it has a better CO2 footprint than grain fed beef (and that not by much, as has been pointed out)