a single page impression can have many hits. i.e. it count all files that web page linked to. i.e. if you have 20 imges on page it would be 20+ (some of other files if any) will be 20+ hits total
Hits don't mean anything in regards to adsense. You probably had a lot of robot activity. Look at awstats and see how many visitors/pages you had. You'll probably see it very close to what adsense is reporting - and that depends on how many ads you are running per page.