Allah's Messenger (ﷺ) gave us the option (to remain with him or to be divorced) and we selected Allah and His Apostle . So, giving us that option was not regarded as divorce.
Sahih al-Bukhari Book 68, Hadith 12
← Previous Hadith A man divorced his wife thrice (by expressing his decision to divorce her thrice), then she married another man who also divorced her. The Prophet (ﷺ) was asked if she could legally marry the first husband (or not). The Prophet (ﷺ) replied, "No, she cannot marry the first husband unless the second husband consummates his marriage with her, just as the first husband had done."

Sahih al-Bukhari Book 68, Hadith 11 Next Hadith → I asked `Aisha about the option: She said, "The Prophet (ﷺ) gave us the option. Do you think that option was considered as a divorce?" I said, "It matters little to me if I give my wife the option once or a hundred times after she has chosen me."

Sahih al-Bukhari Book 68, Hadith 13