For example, if a person creates an application that they open-source under a license that says you can use this code but you cannot sell it, has that person just bound himself to not selling it now as well?
A license is the owner assigning rights and responsibilities over their intellectual property to a third party. Assigning one set of rights in one license does not preclude them from assigning a different set of rights and responsibilities to another third party.
This is how software products come to be dual-licensed or multi-licensed. Each license grants certain rights but imposes its own restrictions. Thus a software house may opt to release a software product under GPL for free, requiring derivations to be provided with source code, and under a closed source license, for a fee, where derivatives can be supplied without source code.