Whenever researchers talk about any mental disorders you need to add the phrase "...which interferes with their day to day life, and causes harm or distress".

These people are not eating healthily, they have an obsession with "healthy" food that interfere with their day to day life and causes harm or distress.

That harm may be from something like REDS (Anna Boniface has written useful stuff about that), or it may be over-training or food restrictions.