One metaphor is to call the model a person, another metaphor is to call it a pile of words. These are quite opposite. I think that's the whole point.

Person-metaphor does nothing to explain its behavior, either.

"Bag of words" has a deep origin in English, the Anglo-Saxon kenning "word-hord", as when Beowulf addresses the Danish sea-scout (line 258)

"He unlocked his word-hoard and delivered this answer."

So, bag of words, word-treasury, was already a metaphor for what makes a person a clever speaker.