Kind of mysterious not because the total accumulated amount in very short time just due to the transaction history.
I checked the TX history the address received 1700,1750,1800,1900 multiple times which made me curious whether it is some kind of salary for their job or what. And after a while it received only dust amounts.
not sold a single satoshi.
Actually no, because you can see the address spend
0.25000000 BTC.