Nobody has given us more than scraps of the story, which makes it so maddening. Because it’s almost like an ink blot test. Whaddya wanna see? It’s there if you look hard enough....
Maybe only AFTER they saw Philando, stopped for some other reason, did they believe that he was suspicious in that manner, which would mean that they had heard the news about the crime and learned the description of associated suspects, in some other fashion.
But again identifications in such encounters are known to sometimes be wildly erroneous. Like in the Amadou Diallo shooting, which felled a fellow with a melon shaped head when the actual suspect had an inverted pear shaped head.
You could just play the audio and learn.