In her journal Mary Jane Chadick mentions 159 Confederate officers and men who were aboard a train in town when Ormsby Mitchel's troops entered Huntsville. Many of these were wounded being transported from Corinth following the Battle of Shiloh. She and other ladies of Huntsville asked permission to care for Confederate wounded. There is no mention of a train wreck or any Confederates already being in town due to illness or injury.
http://www.amazon.com/Incidents-Civil-Journal-Mary-Chadick/dp/0970736819

The editor mentions that General Maxey passed through town a day or two earlier with three regiments and a battalion. I don't have the identities of these commands.