It actually does not use the contents of the battle log and it's because of this lack of checking against it that ghosted actions slip through and count towards the damage total in a given report when they should not. What it uses is a particular message sent which is the basis behind how all the net logs are generated. This message is technically saying "this is what will happen", not "this is what has happened". In other words there is a time difference in when that data is received vs when the damage is confirmed in game. If Bahamut despawns before this confirmation happens, while the damage data is recorded the damage never happens in game.
Even in cases of a "recorded 12 ww" in almost every case one action has to give way. Whether that's a wyrmwave or an akh morn. Now if you are interested in how you can check in game to see if an action was ghosted or not against a log, count the damage entries and/or count how many "Demi-Bahamut casts" messages. If you're in The Balance discord I have the checks pinned in smn_questions.
Addendum: Comparing Summon time with final Bahamut action time from what you linked from your report.
00:01:37.043 for Summon Bahamut
00:01:57.094 for his final Wyrmwave. That WW was certainly a ghost. The time is too close to when the despawn happens, in recorded ms it's actually after 20000ms has passed.
00:03:28.808 for Summon Bahamut
00:03:48.439 for Akh Morn. You ghosted Akh Morn in order to get that 12th ww!!
00:05:25.913 for Summon Bahamut
00:05:45.699 for his final Wyrmwave. Again, like the first summon case due to the timing.
This is a field that has been researched extensively. So please, when we say avoid the 12 ww meme so that you can achieve consistent real damage, take that advice to heart. You're not playing optimally this way. There's a good reason the recommended count is always 11 real ww + 2 real akh morns.