This actually perfectly qualifies as being open source.

No, it doesn't: http://opensource.org/osd

> Open source doesn't just mean access to the source code. The distribution terms of open-source software must comply with the following criteria:

Tarsnap also doesn't claim to be open source: http://www.tarsnap.com/about.html

> While the Tarsnap code is not distributed under an open source license,

Ah ha, thanks for the further correction! Well that makes me feel better about the likelihood of someone taking Colin's work and profiting handsomely off of it.