I wouldn't be surprised at all if this is the right size. Skyrim's install was only a little over 6 GB and everyone freaked out over that beforehand too. Todd Howard has come out a few times and said that they're just very good at managing space and compressing things. They also only continue to get better with games, so even though they pack more into each game, they have become more efficient at managing their install sizes.
Not a lot of companies care about the install size in the same way, but it definitely is possible. Overall, I'd say it's nothing to worry about if it is true and actually serves as an impressive accomplishment for Bethesda.
Edit: Please ignore this entire post, I totally misread the file size.