If you compare what Abu ’l-Fatḥ says elsewhere, it is apparent that he does not say large numbers of a Dosithean sub-sect in Alexandria were wiped out. Comparison of his style and method with other passages shows that he says the leaders of one sub-sect were wiped out. (Or more exactly, this is the style and method of his source. This is the same source that was known to Origen secondhand in fragmentary quotes out of context which he did not understand). Compare what A. F. says about one sub-sect being wiped out when the roof fell in when they were ALL gathered. Similar stories are quote for the end of other sub-sects of the Dositheans. There is also the analogy of Origen saying there were only ever thirty Dositheans,, as well as Origen’s statement that Simon had thirty followers. Notice that in all cases a group founded by a named individual is involved.
In the standard references, you will find A. F. quoted as saying that Bustanos came up out of the sea and killed these people. Then there are guesses that this might be Poseidonios (Poseidon). A Samaritan author would not attribute an event to a Greek god! The rationalising interpretation that a tidal wave might be meant is no better, since no Samaritan would call a tidal wave a manifestation of Poseidon. You have to bear in mind that when A. F. is quoted, it is always according to Vilmar’s edition of 1865. This was a good start, but Vilmar frequently guesses and prints what is not in any manuscript without telling the reader. Very often he follows his ms. C against all the others because it is the oldest. It is not the oldest by very much, and it is badly copied. Guesses about what A. F. might have meant are futile unless the mss. are checked. Both Haroutun Jamgotchian (of Yerevan) and myself have published careful studies of the readings of the mss. in difficult places, and this fact is quite clear from our samples (Textproben). The correct reading in this case is not Bostanos but Botanos. (The insertion of the S is an easy reading mistake with Arabic script). This means hippopotamus. When A. F. says they had moved from Alexandria to the edge of the sea, it must be remembered that the Nile is the only river called The Sea in Arabic. As A. F. says the place was remote from people, I would guess it was on the Nile delta away from any town. (A location a long way upstream, past Elephantine, is unlikely. This would have been too far from Neapolis. In the Nile delta they could be out of the way but not far in miles from towns and main roads and a port). Perhaps only the leaders moved. Remember what was said about only the leaders being wiped out. We are told some were imprisoned. When they were wiped out, they were probably about to immerse themselves, at least in the imagination of the source author. As for the believability of the story, this is not a question. What A. F. says about the end of the other sub-sects is just as fantastic. In each case, his source wanted to show that they had been wiped out by the hand of Providence because of their wickedness, and being wiped out other than by the hand of man proved how wicked they were. The Dositheans did not vanish from Egypt, only the leaders of this sub-group. There is a notice in Photius of a substantial number of Dositheans in Alexandria in 588 A.D., numerous enough to petition for official recognition as a denomination other than the rest of the Samaritans.
For the same reasons as outlined, be very sceptical about the accuracy of the name Iulianus in this story. Vilmar has had difficulty with the mss. I don’t know yet what the correct reading is, as I have not fully collated the mss. here yet.
A sample of what appears in the Real Messiah order it here
