All the people—believers, hypocrites, and outright unbelievers—acknowledged this; no one ever claimed that the moon had not split, nor did anyone dispute it.
Sahih Muslim records that ʿUmar ibn al-Khattāb (may Allah be pleased with him) once asked Abū Wāqid al-Laythī, “What did the Messenger of Allah (may Allah bless him and grant him peace) recite in the prayers of al-Aḍḥā and al-Fiṭr?” He replied, “In both he would recite, ‘Qāf. By the Glorious Qur’an’ (Q 50:1) and ‘The Hour has drawn near and the moon has split’ (Q 54:1).”
It is plain beyond doubt—given normal human behavior—that had the moon not truly split, those who believed in him would have been the first to reject the claim, let alone his enemies among the unbelievers and hypocrites, especially when he was reciting this verse to them at their largest public gatherings.
Furthermore, it is well known that Muhammad (may Allah bless him and grant him peace) was among those most eager for people to believe him and follow him, and he was the most knowledgeable of mankind about leading people. Had the moon not split, he would never have announced it, recited it before everyone, cited it as proof, or made it one of his signs. Even someone with the slightest political sense would not build his greatest evidence on what everyone knows to be false, much less proclaim it in the presence of the largest crowds.