Where is that information from? There is a lot here that hasn't been released yet, and the devil is in the details.
Regardless, there are at least four ways to get more than one discharge or more than one projectile in a revolver with just one pull of the trigger.
1) Sympathetic discharge of OTHER loaded chambers in the revolver cylinder following firing of the proper chamber. More common with cheap weapons and .22's, but also with old ball and cap revolvers. Always a possibility with any revolver, though, especially if poorly maintained. See for example https://www.bevfitchett.us/gunshot-wounds/sympathetic-discharge-of-rimfire-firearms.html
2) A double load in the fired chamber, either intentionally or from previous misfire. Obviously more common with black powder hand-loaded chamber, as modern cartridges couldn't accept two proper cartridges in the same chamber. Now you could put a full small or medium caliber bullet or cartridge in a long chamber ahead of a proper round (think The Judge .410 shotshell/.45 LC cartridge cylinder, with a .22 or .25 bullet or cartridge ahead of a .45 LC cartridge, for example). https://www.taurususa.com/revolvers/taurus-judge-series
3) A squib, or primer-only discharge from a previous shot, with the bullet or wadding or whatever still lodged in the barrel (no discharge of the gunpowder, just the primer, giving enough gas to push the bullet or wadding out of the cartridge, out of the chamber, and down the barrel a short distance, but not enough force to send the object(s) out of the barrel). If the barrel is not cleared, these objects could become the additional projectiles for the next shot, whether a live round or a blank (if the barrel doesn't blow up in the hand of the person firing the second shot).
4) An improperly aligned cylinder (poor maintenance or damaged), making the fired chamber not send the gases or projectile into the forcing cone and down the barrel, but rather, striking the edge of that cone and/or the handgun frame around the barrel, splitting the gases or projectile into two or more pieces/streams, with some materials going away from the cylinder in a direction different than the pieces/stream still going down the barrel. The cone or frame of the gun can also be damaged this way and become secondary pieces of metal flying away from the gun with force.
When I heard that two people had been injured, I assumed it was a shotgun or rifle.
A revolver would make some sense, because that is what happened with Brandon Lee: A blank behind a squib from a primer-only “dummy” round.