the seller lists that as a "Gary Fisher /Bianchi" so it seems to me they may not know what the bike brand is
It's definitely early 80s.. reminds me of a stump jumper to be honest, but im not sure if they came in that color. The fact it's got reflectors suggests to me it was a production bike. Sincerely doubt it's "20 pounds" especially with the reflectors, kickstand and what look like modern bmx pedals
the price is high unless you're deep into collecting early mtbs.. even then it's probably high.. be nice to see better pics w/ drive side