From the linked article.
“In a Facebook follow-up post, Alvarez-Rodriguez uploaded a video showing that the rifle does indeed fit inside the bouncer box. And the rifle itself, which looked in the fuzzy Twitter photo like it might be just an airsoft gun, sure looks like the real deal in the full-resolution photos. I can’t explain why there’s also a box of 9mm rounds and a pistol magazine sitting next to the Mossberg, but whatever the reason, that’s my kind of baby shower.”
Also I doubt the people there would mistake a toy gun for the real thing,
To her credit, Alvarez-Rodriguez also said the Mossberg was “a total shock,” but that it was “hilarious, and just glad it came into safe hands with all of our husbands being military.”