I went to Isle of Giant with my level 120 Vulpera Hunter to get the tome to learn how to tame Direhorns, but when I tried to use it the cast ended with an error message saying that the tome wasn’t for my character. So I went up to a Direhorn to tame it to see if Vulpera had the skill baseline like Zandalari Trolls. I got an error message saying I didn’t know how to tame them.
Just in case I switched to my level 120 Mechagnome Hunter to try it out too. Same result, can’t learn the skill and can’t tame Direhorns either. Both could learn to tame Feathermanes though, so my guess is that the Direhorn tome was forgotten and both new races weren’t added to it.