You actually enlist in the USMCR when joining the PLC program. It appears he only spent some or part of the 6 week PLC Junior increment and then dropped out, which is the beauty of the PLC program as most of the attrition comes from those who decide not to return for their second, or Senior, increment.
If you drop out you are given an honorable discharge from the USMCR.
This reminds me of Dan Rather and his claims of being a former Marine.