All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Merely searching that phrase out of curiosity does not make a Muslim a disbeliever. However, searching for that phrase – whatever the motive is – is a heinous and very dangerous matter.
It must be avoided, and over time, it may lead a person to applaud belittling the Prophets, or wishing to do that, or being pleased with it, and this is undoubtedly disbelief.
You should advise him to stay away from pornographic sites and explain to him that it is forbidden to enter them for any reason.
Allah knows best.