In Odyssey 3, Nestor was telling young Telemachus tales about the adventures experienced by the Achaeans after their capture of Troy. Some of the tales involved the brothers Agamemnon and Menelaos. In the context of those tales, there was a mention of the island of Lesbos at O.03.169. And now in Odyssey 4, we get to know more about the adventures of Agamemnon and Menelaos after Troy, but here it is Menelaos himself who is telling tales about these adventures, and, in his tale, there is a detail about Lesbos that contradicts the tale told by Nestor in Odyssey 3.
Here I epitomize from Nagy 2015§§ 77–78:
[§77] While telling his tale to Telemachus in Odyssey 4, Menelaos expresses a wish that the young man’s father, Odysseus, will return to Ithaca and will defeat the suitors of Penelope—just as this hero of the Odyssey had once upon a time defeated an opponent named Philomeleides in a wrestling match that had taken place on the island of Lesbos, O.04.341–344. The verses here at Odyssey 4.341–344 are repeated at 17.132–135, where Telemachus retells to Penelope the story told to him by Menelaos.
[§78] In terms of what Menelaos says at O.04.341–344, he was in Lesbos when Odysseus performed his heroic feat there. There is some agreement here with the narrative of Nestor at O.03.168–169, who says that Menelaos had sailed from Tenedos to Lesbos. So too had Nestor himself and Diomedes sailed to Lesbos, and they were already there by the time Menelaos arrived. See the comment on O.03.168–169. But the problem is, Odysseus himself did not sail from Tenedos to Lesbos in the narrative of Nestor: rather, as we saw at O.03.160–169, Odysseus together with a sub-group of Achaean followers had already sailed from Tenedos back to Troy in order to rejoin Agamemnon, who was still there at Troy, O.03.160–164, while Nestor and Diomedes together with their Achaean followers sailed on from their stopover at the island of Tenedos and arrived at the next stopover, which was the island of Lesbos, O.03.165–169. There, at Lesbos, Nestor and Diomedes were joined by Menelaos, who as we saw arrived later, O.03.168–169. In short, the parting of ways for Odysseus in Odyssey 3 had already happened on the island of Tenedos, when he had left Nestor and Diomedes and Menelaos in order to rejoin Agamemnon. Here in Odyssey 4, by contrast, Odysseus seems to be still present in Lesbos when Diomedes and Nestor and Menelaos are present in Lesbos. And that is how Menelaos could have witnessed the victory of Odysseus in a wrestling match at Lesbos.