They aren't really comparable though. C the language was really only comparable with part of Smalltalk, and the parts of Smalltalk it was comparable with were pretty portable. It's the rest of Smalltalk, the operating system interfacing stuff and the like, that C didn't even have. You had to rely on external libraries for that stuff, and they weren't particularly portable.

You could write perfectly portable utilities in Smalltalk as long as they didn't rely on any services that were not comparable to what C the language contained within itself.

Wouldn't "trying to port an app" mean trying to port between different C gui libraries?

(Just like "trying to port an app from one Smalltalk to another" would mean trying to port between different Smalltalk gui libraries.)