A really bad one.
The Martian Race had encountered the people of the fifth planet, grokked them completely, and had taken action; asteroid ruins were all that remained, save that the Martians continued to praise and cherish the people they had destroyed.
This quote doesn’t define the word, though. As per the article, Grok means “to understand completely” not “to obliterate”.
After the Martians grokked them, they realized there was no option but to obliterate them. This is possibly a valid response, depending how terrible the occupants of said planet were.
It’s still a bad name for a chat bot, as they clearly do not understand anything completely, or at all.
According to the book, grok is the Martian word for “to drink”. Since water is rare on Mars (and it is needed for life), it is a holy substance. Martians (and people studying the Martian language) share a drink of water to become “water brothers”, bathing is a profound ritual and to understand something or somebody completely is referred to as “drinking” them or it.