Hello!
Meaning: A grocery bagger is the person who in a supermarket or grocery store who puts the items into the bag once they have been scanned. Is this viewed as an ideal job? (No). Therefore Talia does not want to be given this title.
You can also see a level of colloquialism due to "It is not like"; giving the sentence a slight sarcastic tone, thus saying that Talia Randle did not want to have the title of fastest grocery bagger.
A small correction that I would use:
It is not like Talia Randle grew up dreaming of *becoming* the fastest grocery bagger in the West.
Being is a state while becoming implies a transition from one state to another.
And a small fluidity correction:
"*It's* not like Talia Randle grew up dreaming (etc)"
Since it's colloquial, I naturally would use the contraction.
Not my cleanest explanation but I hope this helps!