How would Gombrich have correctly deduced Hitler's death by hearing the Bruckner symphony?

Bruckner was VERY popular among the nazis. For them, the three greatest musicians who represented all that was great about German music were Ludwig van Beethoven, Richard Wagner, and Anton Bruckner.

Bruckner's music was played at important events, and they were very fond of his music and his image. Here's a picture of Hitler unveiling a bust of Bruckner at Regensburg in June 1937. Here's Joseph Goebbels' Address at Regensburg.

Why were they fond of good old Anton? Well, he was born in Austria, from a family of "simple people." He was not a child prodigy and didn't really become a super star in his life time. He kept his head down, worked hard, and didn't particularly great recognition in his lifetime. Unlike other famous composers, he was not a megalomaniac asshole, he was apparently humble. He became famous after his death (and the nazis kind of helped getting his music played more often). This fits with nazi propaganda: An Austrian guy who came from humble roots, worked hard, and took the German greatness to new heights, leaving the people an amazingly great legacy without while keeping his humility. Yep, good Adolf... I mean, Anton... Yep, Bruckner made a good poster boy. The nazis used his image and touched up his biography to fit their agenda.

Now, why his music? Well, Bruckner composed massive orchestral music, which is a very German thing. Great composer of symphonies, with a mostly conservative taste (even if there are some peculiarities in his music). Bruckner was very fond of Wagner, and studied his music a lot. You know who else was a super fan of Wagner? Hitler.

Bruckner wasn't super famous in his lifetime, and he had quite a few critics. See, there was the so-called War of the Romantics. When Bruckner took the Wagner side, the Brahms side went against him (including Eduard Hanslick, who was a very influential critic). I think the nazis twisted that later to say the enemies of German greatness conspired to avoid his success (guess who those enemies would be?)

Why use that particular music for the announcement? Bruckner worked in that symphony between 1881 and 1885. It is dedicated to Ludwig II of Bavaria, a fan of extravagant art and architecture and the biggest Wagner groupie ever. Bruckner wrote the second movement for Wagner as some kind of tribute, fearing Wagner would die soon (he did die soon after he started working). He included Wagner tubas in his orchestration.

That Adagio has the indication Sehr feierlich und sehr langsam (Very solemnly and very slowly). And it can be considered solemn, sad, dramatic, powerful music. Composed in an unmistakably German style, originally for a very influential German genius, who Bruckner admired a lot. It was meant to be a respectful and sober homage, I guess we can agree it gives that vibe.

The Adagio was played before announcing the defeat at Stalingrad, and then to announce Hitler's death. Apparently the recording used was conducted by Furtwängler. So, listening to THAT music again, after a lot of super dramatic Wagner and frequent calls to attention... It was obvious something VERY VERY VERY BIG had happened.

Were there other possibilities other than Hitler's death? I don't know, I leave that to the people knowledgeable of WWII history.

Some words about Bruckner's music after the nazis.

Bruckner's life and music was studied, and the stuff the nazis tried to make up/revise was discovered. His status in the orchestral canon was maintained or even increased. He might not be a household name like Beethoven, but his music is extremely common in the concert hall and most people attending symphony concerts will recognize his name and music (not to mention any music student of the last 4 decades). He is as representative of symphonic music as it can get.

Unlike Wagner, Bruckner and his music have not been associated with nazism and/or antisemitism. Wagner was vocal about his antisemitic ideas, and many other things (kind of a megalomaniac and an asshole). As far as I know Bruckner never expressed anything of that sort. Wagner's music has not been well received in Israel, but as far as I know they have had no problem with Bruckner.

In the last decades no respectable/sane conductor/orchestra would omit his symphonies. Bruckner's music was not particularly popular in Austria during his life, but they fully embrace his music now.

TL;DR

The nazis liked Bruckner and his music very much. They had used the same music to announce the defeat at Stalingrad, and it was kind of natural to assume something big had happened after listening to a lot of dramatic Wagner and that specific Bruckner.