The contradictions

While the German Fokker’s attacked Bill Johns he noticed a second drama that nearby German fighters shot down a De Havilland DH 9 in flames in a similar attack.
Later, German pilots told Johns, that the pilots of the DH9 were sergeants but no names were given because their bodies had been burned beyond identification.

Two DH9 were claimed that same day in that general area. Lieutenant Stephan shot a DH9 near Gremersheim and Sergeant Metzger shot a DH9 near Landau. Both Germans belonged to Jasta 70. There is no time of the crash on both kills available.
It is very unlikely that Bill Johns could have seen one of these DH9’s because of the distance.

Later Bill Jones stated that the famous German Air Ace Ernst Udet shot him down. Udet was on leave the 16th and returned to his squadron, Jasta 4, first on 19th of September 1918. Jasta 4 was also operating from the aerodrome Busigny-Escaufourt in North West France!

Oberleutnant Ernst Udet. German Air Ace with 62 kills in WW 1
Bill Johns used Udet as example for his Erich von Stalhein creation in his books later on.

Who really shot down Bill Johns?
Lieutenant Georg Weiner claimed the shot down. The CO of Jasta 3, which operated from the Gross Tanchen aerodrome with Fokker DVII fighter planes, was officially accredited with the kill over the village of Alteckendorf which is only a few kilometres away from the Village of Ettendorf were Bill Johns later that day was locked up in a schoolhouse cellar for the night.

Leutnant Georg Weiner. German Air Ace with 9 kills in WW I

Another German Pilot had also claimed the kill. This was Sergeant Emil Prime (In some books called Eduard) from Jasta 78B who also flew a Fokker DVII which operated from Buhl aerodrome.
He and Weiner, and maybe other pilots, must have visited Bill Johns in the schoolhouse.
Johns later stated that the officer, who had shot him down, wore the Bleu Max medal around his neck.
The archives and sources up to now show no record of Weiner that he was awarded with the Bleu Max. (Pour le Mérite)
Officially the Germans reported that the plane was a DH 9 with serial number F5712 but there was no such DH9 with that serial number. The serial number belonged to a DH4.

Officially Leutnant Weiner shot Bill Johns but there will be always the possibility that Johns was shot down by both Weiner and Prime.
Why Bill Johns mentioned the crashing of a DH9 at his starboard will be insoluble. The two mentioned DH9’s crashed about 60/70 kilometres to port behind him. He could never have noticed that from his position.
Bill Johns ended up in a P.O.W. camp till the end of the Great War.