many things stated in the article are mis-stated and i'm worried the article does more harm in confusing readers than good. not everything written is false, although quite a bit certainly is, but even if it is correct its written in a confusing way that is not easily understood.
a few general points...
1. the list of headphone form factors is not accurate and is misleading. some categories you list are instead general properties that can apply to any headphone while others are subtypes and in some cases subtypes are not broken down.
2. open and closed is not a headphone form factor. this can apply to any headphone form factor. also being open or closed does guarantee an effect on sound quality although it does often have an impact on soundstage, bass and clarity but not always in a bad way.
3. headphone size does not affect how accurate or how good sounding they are. in fact, some iems have better noise isolation, bass levels and sound quality than headphones double their price while being easier to drive.
4. soundstage does not depend on headphone size. headphone design, earcup size, pad depth, open vs closed and other factors affect this. also bigger soundstage does not always mean better sound quality or experience.
5. passive noise cancellation is a feature of closed designs, not a form factor or type. yes, some may be more isolating than others.
6. 3d is more of a subtype. any can use virtual surround to get an effect though many do not have it built in. likewise there may be a limit on any true multi-driver headphones but the possibility exists for both on ear or over ear to use this technology.
i could write more, but if you would like a better list henry, send me a pm over on TH.
This guide is not meant to be read as a list of form factors, but of differentiating features of headphones, as in a glossary. Nowhere in it does it suggest that a pair of headphones can only include one of the listed characteristics.