saw a tacoma door sill rust.. weird..

Saw an 02 Tacoma today.. The body is pretty much rust free but I found some rust bubbling up in the door sill, at the point where the plastic floor board meets the metal body. Is this kind of rust common and does it indicate more trouble down the line?

 

i've seen this on other cars. water gets in there when it rains. it runs down the windows and into the door. if the little holes around the bottom of the door get clogged up water can sit in there and give you bonus rust.