The underlying MAXFLOW code has its own license restricting distribution and use. See graphcut code. To give an imperfect summary: the underlying code is restricted by a research only license. Read the MAXFLOW license in src/outside/README.txt for more information.
PyGraphcut is a derivative work from MAXFLOW. As such, in using it you are subject to the license of MAXFLOW. PyGraphcut has no usage license terms of its own, however. The implication is: you are licensed to use PyGraphcut if and only if you are licensed to use the underlying MAXFLOW software.
Note that the copyright for the code is distinct from the usage license. All code and content within the PyGraphcut distribution archive outside the src/outside directory is copyright Thomas Finley at tfinley@gmail.com, while all code in src/outside is copyright of their own authors (in most cases either Boykov or Kolmogorov).
To summarize: the license is research only, but if you manage to get a relaxed license out of V. Kolmogorov, feel free to use PyGraphcut subject to the terms you negotiate with him.