Joe Russo included himself in a cameo role in Avengers: Infinity War as a paparazzi photographer trying to get shots of Tony Stark in a scene that was ultimately cut from the film, so it’s not like Russo’s own cameos are that important.
The intentional secrecy with which Russo announces the cameo certainly makes it sound like this might be more than a simple cameo, but that’s just speculation.
It’s not like the Russo brothers don’t enjoy messing with the fans.
He could have just as easily given his daughter a similarly minor part.