Actually its not.
Legion has been out all 2 years, the forgotton was found a month after legions launch and for atleast a few months was just impossible to get with how many people.
You do not allways know when the thing is going to spawn or if it has spawned, unless he is literally logging on at 6 hours and flying around looking until they spawn.
It is literally on the level of people farming the time lost protodrake and giving it to people, yes more common, but still the same issue of you cant just log on every 6 hours and know it will be there, you have to wait and camp and fly around.
so literally to have done it 100 days means literally he would have to spend ATLEAST about a year spending hours every day just looking for this thing. I have spent ALOT of time in azunsa, i have allmost 200 days played time in legion, and yet i have seen those crystals 5 times and got the mount on third time.
now imagine doing that 100+ times and EVERY ONE OF THOSE TIMES being able to find them, then bring a person in