There is less debris around on the way to mars and this is a known and worsening for the ISS due to its age.
Corrosion is a hard problem in living quarters (ie moisture and salt) in space (sealed with no gravity)
Don't forget the module we're talking about was built in the 80s originally intended for MIR 2. It's been in service since 2000.
Anything larger, say a lost screw driver, would punch thru the ISS like it wasn't even there leading to some ugly consequences.
The ISS can dodge debris by adjusting the height of its orbit.