Everyone makes mistakes, and if you’re a record producer, that might include hiring the wrong musician to play a very important part.
The recording in question was of Camille Saint-Saëns’s The Carnival of the Animals. The composer calls for the glass harmonica in the “Aquarium” movement to impart swirling, aquatic moods, indicated in the score as "armonica." But as Norman Del Mar points out in Anatomy of the Orchestra, the word “harmonica” isn’t without ambiguity. According to a 1984 dictionary of musical ephemera by British musician and journalist Fritz Spiegl, this detail might have been lost in translation:
The more down-to-earth name [of the harmonica] avoids further confusion with the GLASS HARMONICA, a muddle perpetuated in a gramophone record of Saint-Saëns’s Carnaval des Animaux. The record producer must have seen the word Armonica in the score (by which the composer meant the eerie, liquid sounding glass harmonica for the Aquarium movement) and engaged Tommy Reilly to play the part on the mouth organ.
Details about which recording that refers to are hard to come by, but it could very well be the one above, which features the Czechoslovak Radio Symphony under the direction of conductor Ondrej Lénard. Skip ahead to 2:56 to hear for yourself.