A federal judge delivered a pair of legal setbacks to the tech billionaire Elon Musk this week, rejecting Mr. Musk’s attempt to throw out a defamation lawsuit brought against him by a British cave explorer whom Mr. Musk had accused on Twitter of being a “pedo guy.”

The judge, Stephen V. Wilson in United States District Court in Los Angeles, also ruled that the explorer, Vernon Unsworth, was not a public figure — meaning the bar will be lower for him to prove defamation.

Judge Wilson ordered Monday that a jury trial begin on Dec. 3. He denied Mr. Musk’s argument that the case should be tossed because his statement, a shortened version of the word pedophile, was a throwaway insult not to be construed as fact.

Mr. Musk had also argued that Mr. Unsworth was a public figure because of his participation in a high-profile rescue of a youth soccer team trapped in a cave in Thailand last year. Public figures need to meet a high legal bar called “actual malice” — essentially knowing a statement is false when the statement is made and making it anyway — to prove defamation.