While Donald Trump hailed the outcome of trade talks in London, Xi Jinping walked away with an understated strategic gain: a negotiating process that buys China time and helps defuse the threat of more harmful tariffs and technology curbs.

Mr. Trump said in a post on Truth Social that his call with Xi Jinping, China’s top leader, had focused entirely on the trade relationship between the nations, which has soured in recent months in a dispute over the export of critical minerals used in an array of industries.