I believe this is incorrect.
Murphy's sign could be positive in some cases of gallstone pancreatitis with concomitant acute cholecystitis, but it's misleading to include it as an expected exam component for gallstone pancreatitis alone.
On the AMBOSS page for gallstone pancreatitis, there is zero mention of Murphy's sign anywhere, though general RUQ pain and other symptoms are discussed extensively.
Unfortunately, AMBOSS doesn't specifically say one way or the other. Other non-AMBOSS sources I've looked at all agree that Murphy's sign is specific for acute cholecystitis. DeVirgilio's surgery, in particular, explains that gallstones which cause gallstone pancreatitis are, by definition, small enough to have already escaped the gallbladder and they usually also escape the biliary system entirely so wouldn't themselves cause cholecystitis directly or indirectly (page 230). One could have more gallstones and concomitant acute cholecystitis, but that's not what this card is about.