Shares of Kroger were more than 9 percent higher Thursday, trading around $26.70, after the company reported higher-than-expected fiscal third-quarter earnings and upbeat same-store sales. The company said aggressive discounting lured more customers to its stores.
"It's incredible. You'd think they must be getting taken over," Cramer said on "Squawk on the Street" about Kroger's stock rise.
Earlier Thursday, Kroger's chief financial officer, Michael Schlotman, told CNBC that the company's results are a reflection of its work to "redefine the grocery shopping experience."
The Cincinnati-based supermarket chain, which also owns Ralphs and Harris Teeter, has been lowering prices at its stores and has sought ways to work more with local brands. That comes as it faces competition from Wal-Mart and a merged Amazon and Whole Foods.
"There were a lot of people short Kroger," said Cramer, the host of CNBC's "Mad Money." "They didn't understand that Amazon tomorrow is not going to wreck Kroger's margins."
"'Death Star' is going to hurt things," Cramer said, referring to Amazon. "But you have to see the whites of their eyes. I mean they didn't destroy Kroger the moment they bought 400 stores of Whole Foods."
Cramer said if he were Kroger, he'd be more concerned about Wal-Mart. "Because, Wal-Mart is the biggest grocer," he said. In October, Wal-Mart announced changes to its grocery business, including plans to add 1,000 online grocery pickup locations at its U.S. stores in fiscal 2019.
— Reuters contributed to this report.