‘he is a “dumba”.’
I looked this word up. Matt Dumba gets a lot of hits; he’s a Canadian ice hockey defenseman.
The other major usage is:
Define dumba: a fat-tailed sheep of Bokhara and the Kyrgyz steppe.
Not sure what the woman was trying to say; it doesn’t appear to be an insult. Maybe a fat-tailed hockey player?
Maybe it was truncated and the “ss” was left off out of politeness.