By not disabling the cache Safari will just reload the web page from disk, instead of downloading it all over wifi. In normal use you don't sit around reloading the same page all day, you surf to different web sites, so caching extends battery life to unrealistic levels.
"Not disabling" isn't the same as "enabling".
More importantly, the bigger point is that Consumer Reports dismissed the fact that battery tests with Chrome on the Macbook were both consistent and long with "we use the default browser on the operating system" as a justification for not updating their review, but now we find out that they also modify the default browser from its default mode... something they didn't report at the time.
So, which is it, default or not? They can have it both ways if they report all of the details of their tests, but they can't simply say "we always use the default (except when we don't)" while retaining any sort of credibility. The fact that they refused to repeat the tests with witnesses present, and now we find out that they changed an additional variable without telling anyone means that we can't trust them, at least until they've built that credibility back up from scratch.