Rust on bottom of opening to bedrooms

[Jennifer MacDonald]

Anyone know why rust type residue would be on the bottom of the opening to the bedrooms (pic attached)?  There is no actual door in this location just a cut out in the wall that leads to the bedrooms.   You can see it at the very bottom of the opening at the baseboard level.  I saw this in person and touched it-feels like rust.  Maybe a metal band about the opening to texture the wall? 

Any help appreciated!

[Wayne Brooks]

Sheetrock corner beads are typically metal, but usually zinc/galvanized.  Obviously have in contact with water, possible interior flooding.....are those wood floors new?