I just visited the Chrome store and chose the first extension: https://chrome.google.com/webstore/detail/office-online/ndjp... It makes word documents AND spreadsheets?!
Hopefully you can see where I'm going... whatever's written in the policy is difficult to enforce literally. Someone has to make the distinction based upon the intent of that policy. A person has to draw the line. If Google have made the decision based on that policy, well that's their decision.
Reading https://developer.chrome.com/extensions/single_purpose (part 4) makes me thinking "disrupting ad networks" could be that single purpose. Then it'd cover blocking & clicking. Just like "Office Online"'s "edit office documents" covering both "word processing" and "spreadsheets".