IANAL, so I couldn't tell from the TOS if API use like this is acceptable or not, but at least on the "root page" of app.imdb.com, they say:
For use by clients authorized in writing by IMDb.
OP: Did you ask for authorization?
For use by clients authorized in writing by IMDb.
OP: Did you ask for authorization?
'copyright': 'For use only by clients authorized in writing by IMDb. Authors and users of unauthorized clients accept full legal exposure/liability for their actions.'
Since he is using the API key taken from the official app (see: https://github.com/maddox/imdb-party/issues/8#issuecomment-1... ) i really doubt he got anything from them.