Actually, I agree. We originally used the term "platform". But, we found that people understood more easily when we switched to "operating system" -- and it's not too far off the mark, honestly. Sandstorm is an OS in the sense that Android is an OS. Both use the Linux kernel, but largely control the userspace. (Sandstorm can run along-side your existing Linux distro without interfering with anything, but it doesn't really use any of your distro's infrastructure so this is somewhat of a technicality.)
The problem with "platform", which surprised me, is that a lot of people now think "platform" is somehow synonymous with "cloud service". For example, if you watch HBO's Silicon Valley, you may remember the whole "platform vs. box" debate from this season. It's a frustrating perversion of the word, but it is what it is.