I haven't used it myself so I'm only guessing, however I would venture to guess, based on my experience with other products that the reason you are seeing such high numbers is because of the singular/plural and long tail/short tail phenomenon. What that means is that if your keyword was "dog toy," you may be seeing it pull both "dog toy" and "dog toys" as being the keyword. Similarly, you may have long tail keyword usage which is showing up under short tail usage (i.e. "dog toy" would show up even when you use a long tail keyword such as "dog toy for dogs who like to chew").

Finally, it's also possible that it's set to ignore slugs, which Google often ignores. This means that it may find "dog toy" in a sentence such as "I have a dog and toy buying for him is always a nightmare." Some search engines may ignore the word "and" thus creating an extra instance of the keyword even though it's not technically together.

Again, I'm not using Blogger High SEO, mostly because I didn't have the patience to figure out how to install the PHP add in it requires (ion something, I forget what it was called exactly) and my host doesn't offer one click install on it so I'd have to do it manually. Thus, I can only guess at the problems that it's having.

Yeah this is a free plugin