MySQL: Do killed query results get cached?
Yes and no.

The Query cache will not see, much less keep, the partial result.  The page you referenced is talking only about the Query cache.  The QC is populated only after the complete result is built.  This gives a significant boost for a repeat of the identical query.  (Similar queries are not helped any by the QC.)

InnoDB's buffer_pool (and the equivalent in MyISAM) caches whatever blocks are read from disk.  Blocks that were read from disk before the killed was process will probably still be in RAM.  This will provide some performance boost for repeated executions of the same or similar queries, whether killed or not.