Sean Smith was sad to learn Brandon Browner will spend the next 8 years behind bars ... 'cause Smith says the guy helped him when the 2 were in jail -- and the place was awful.
TMZ Sports broke the story ... Browner pled no contest to attempted murder Tuesday -- and was sentenced to 8 years in state prison.
When Smith -- an ex-NFL DB who did time in an LA jail with Browner over the summer -- saw the news .