One of Shazam!'s Easter eggs lays the blame on Lex Luthor (Jesse Eisenberg) for the alien invasion in Justice League! Director David F. Sandberg's superhero fantasy will continue the more fun and hopeful DC Universe that began when Justice League pivoted away from the darker tone established by Zack Snyder. Now, it seems the in-universe scapegoat for Steppenwolf's invasion is the DCU's number one Big Bad, Lex Luthor himself.
Seemingly crazed when imprisoned in Arkham and shaved bald at the end of Batman v Superman, Luthor warned Batman (Ben Affleck) that “the bell cannot be unrung… he's coming!” As it turned out the ‘he' who did arrive was Steppenwolf (not Darkseid), who sought to collect the three Mother Boxes and terraform the Earth into another version of his homeworld Apokalips. The Justice League resurrected Superman (Henry Cavill) and stopped Steppenwolf's invasion in an unnamed Russian town, but the super team was unaware that the bald billionaire staged an escape from Arkham. In Justice League's post-credits scene, Luthor recruits Deathstroke (Joe Manganiello) and revealed his plans to build “a league of our own.”
Shazam! is full of references to Justice League and all of the DC movies that precede it. In fact, Freddy Freeman (Jack Dylan Grazer), the foster brother of Billy Batson (Asher Angel) – who can become Shazam (Zachary Levi) when he says the magic word – is a superhero fanboy who has his own collection of Justice League merch. One of Freddy's prized possessions is a framed copy of the Daily Planet boasting the headline “SUPERMAN IS BACK”. It's a very compelling Easter egg because his “Weekend Edition” of the Planet is a composite of articles describing the events of Zack Snyder's films.
However, the text is the really fascinating part! In the sidebar, underneath “Alien Attack on the World” and “Russia Cleans Up”, it reads: “The Top Suspect: As a worldwide search begins for those responsible, specialists say early signs point to Lex Luthor and his associates.”
Laying the blame for Steppenwolf's invasion on Luthor and “his associates” sheds light on some of Justice League's aftermath. Luthor's escape was naturally news; he was also very vocal about aliens coming when he was incarcerated so it makes sense he is linked to the invasion. Citing Luthor's “associates” indicates that recruiting for the Legion of Doom is further along than just Deathstroke (and these are matters Batman and possibly Cyborg must be tracking – they are likely the “specialists” noted).
Pointing the finger at Luthor and never naming Steppenwolf also illustrates certain decisions that were made regarding what aspects of the truth the League wanted publicly known; Lois Lane and Clark Kent would have known everything that happened in Russia, yet the truth is skewed. Choosing to omit Steppenwolf and his Parademons's names may be a choice made for security reasons: it protects the secrets of Themyscira and Atlantis. To acknowledge the Mother Boxes means revealing the history of Steppenwolf's first invasion thousands of years ago, and that two of the alien power sources were hidden by the Amazons and the Atlanteans – hidden civilizations the world doesn't even know exists (yet).
Finally, while it may seem unfair to blame Luthor for the invasion when he had no actual hand in it (that fans know of), this could also be strategy on the part of the League: it puts the evil billionaire and his malevolent allies on notice that the heroes are onto them.
All this said, it's worth noting that all of this is gleaned from a Shazam! prop that will likely not see more than a few seconds of screen time; and that other excerpts of the newspaper use old and repeated copy (the main stories use the same text about the events of Batman v Superman: Dawn of Justice). Ultimately, Freddy's Daily Planet is merely a cool background detail, but it does hint at some potential direction for the wider DCEU. Fans won't really know what will truly count as canon until Luthor and the Legion of Doom emerge in Justice League 2 – but at least the groundwork for that sequel is clearly being established.