Not Surprising given that all the icons are exclusively based on a combination 2D Shapes and gradients (that includes the game centre icon).
If the symbols matched the clip art symbols exactly then I would say that they were using clip art elements. Given that many of the clip art symbols often needed to be extensively modified i would say that the designers didn't go anywhere near MS clip art elements.
Then again I don't think that the creator of the video was implying that, rather just how flexible MS word can be.
I don't think the video would translate well with some people here though, who will literally interpret it as having Apple having used MS Word to create the icons rather than it being replicable in MS Word.