This isn't a particularly new trick at all. It first emerged on social media back in 2018 and was actually from a YouTube video of a Ben 10 toy (which you can see at the top of this article). That video would suggest that it is saying 'Brainstorm' as it is a name of a character from the animated show.
The truth of the matter is that it is all about acoustic patterns and what the brain expects to hear regardless of the sound that you actually hear. Professor Valerie Hazan, who is a hearing and phonetic sciences expert from University College London is quoted in a 2018 Huffington Post article as saying:
The reason that a person can see their perception switch without explanation may also mean that our ears and brain have latched on to the other acoustic pattern than the one they were previously latching on to.
The video brings to mind the 'Yanny or Laurel' clip which also emerged in 2018 which also caused people to hear two different words. Still, they are yet to cause the uproar and debate that the great colour of the dress picture did in 2015.