Tibetans told VICE World News that the meaning of this common expression used to tease and teach children is completely lost in cultural interpretation and its English translation. The correct phrase in Tibetan for this joke is “Che le sa”, which roughly translates to “Eat my tongue.” English is the Dalai Lama’s second language and Indian news outlets have previously reported that the leader speaks in broken English at public events.

[…]

In a Youtube video, Jigme Ugen, a second-generation Tibetan refugee living in the U.S., explains how this display of affection was born out of a game played between the Tibetan elderly and children. Kids who go up to their grandfather, for instance, are asked to kiss their grandfather’s forehead, touch their noses and kiss them.

“Then [the grandfather] says that I’ve given you everything so the only thing left is for you to eat my tongue,” Ugen said. “The child probably never gets the candy or money but gets a beautiful lesson about life, love and family.”

https://www.vice.com/en/article/jg5854/tibetans-explain-what-suck-my-tongue-means-dalai-lama-viral-video

tl;dr: A harmless translation issue.