The author does not claim it isn't open source, the author claims it doesn't comply with the four freedoms.

> and will need to recompile the source code to create your own binaries.

I believe the author specifically calls out this document themselves, and emphasises the phrase above, as being the problematic portion. And while canonical does also say "For further information, please contact us (as set out below)", they have not clarified this concern despite being contacted and asked.