Yep... Most likely...Sounds like you might have had one stuck in the barrel then fired another on top of it.
A low muffled shot should always be a sign to stop, remove the bolt and check for obstructions.
Or it was simply a case rupture with the second, which can be an unpleasant experience - especially if you get showered with flame/combustion gas!
Case ruptures can be a faulty/weak case that bursts/splits, or a poorly head-spaced chamber in relation to the bolt... But seems to be most often, as I have witnessed, a combination of both poor cartridge and poor quality firearm.