The article does not claim that 'Abdu'l-Baha thought He was Christ, but rather the "WORD". There is a differnce. Jesus Christ was composed of two Beings: the Christ (called the Father or Holy Spirit) and the WORD (called the Son). Jesus said "The Father is in me, and I am in the Father". The article argues that 'Abdu'l-Baha is the return of the WORD/Son, and Baha'u'llah is the return of the CHRIST/Father.
Christ=Manifestation of God=incarnation of a name/attribute of ALLAH, from the World of Names.
Word=the "command" of God, when ALLAH said "BE!" and created the Cosmos, from the World of Command.
The Word became "flesh" as Jesus (John 1:1-2,14), but Jesus was not "Christ" under His baptism when the Holy Spirit (Father) entered Him, and this is why Jesus afterwards said: "The Father is in me, and I am in the Father".
Shaykh Ahmad taught that every Prophet had a RUH (spirit) and NAFS (soul/individuality), and the Ruh and Nafs could "return" as two different individuals, such as the Imaam Mehdi, who returned as The Bab (Prophet) and as a chosen one (Quddus), or the prophet Muhammad whose Ruh returned as The Bab, and whose Nafs returned as Mollah Husayn Bushru'i, who was a "mustafa" (chosen one) but not a prophet lesser or otherwise.
This would mean that 'Abdu'l-Baha was not a "prophet" but a "chosen one". Google "Baha'u'llah" and "chosen ones" and see where He speaks of "chosen ones" and they are "sent" by God as well, but they are not "prophets".
Sorry the link did not work.
The firewalls here are preventing me from accessing the article in question (I may be able to read it later), but I'll simply point out that 'Abdu'l-Baha himself stated he was NOT
a Divine Messenger!