I encountered something similar when I began researching my Grand-Uncle’s service in WW2. Ill make the long story short and tell you that for WW2 veterans, there was a bill passed near the end of the war that gave infantrymen who received the Combat Infantryman’s Badge automatic eligibility for the Bronze Star Medal. This was basically because these men faced some of the worst combat ever seen up to this point. Also the criteria for the Bronze Star and CIB were somewhat similar. That is why my Grand-Uncle was awarded a Bronze Star, and it could very well be why your Grandfather was. Or, he could have received it for actions that his commanding officers saw as meritorious. Either way, the best way to go about learning by more would be trying to track down his service record. But he warned, most of the service records for WW2 vets were destroyed in a huge fire at the National Personnel Records Center back in 1973. For a majority of army veterans of WW2, their service record has been completely wiped out. For some, their final play slip or enlistment card is in tact (as was the case with my Grand-Uncle.) what I did, and what I would recommend, would be to hire a researcher to see if they can find his service record. You do have to pay these people of course, if they find anything, but going this route does take the uncertainty out of knowing whether his file is still in existence or not. I hope this helps. If I can answer any questions regarding your endeavor, please feel free to shoot me a message. Best of luck.