Is saying "Alhamdulillah" before eating a Sunnah taken from the Prophet, may Allah bless him and grant him peace, or was it merely an incident that occurred between him and Abu Hurayrah?

Firstly, the Sunnah before eating and drinking is to say "Bismillah" (in the name of Allah), not "Alhamdulillah" (praise be to Allah). Praise is said after eating.

Secondly, the Hadith of the Prophet ﷺ, in which he praised Allah, said "Bismillah," and drank milk, does not indicate the permissibility of praising Allah before eating or drinking. Rather, his praise to Allah was for the blessing He placed in the milk, as it quenched the thirst of all the people of Suffah without running out.

Thirdly, attributing the recommendation of starting with praise alongside "Bismillah" when eating or drinking to Sheikh Ibn Uthaymeen, may Allah have mercy on him, is incorrect. The Sheikh clarified that praise for eating and drinking comes after them, and his statement about praising Allah at the beginning of matters means that "Bismillah" suffices for praise at the beginning of some actions like eating and drinking, if the Sunnah dictates it.