I see that Kidzsearch already stepped in to help you,
But dont worry, What seems to have happened, is that somebody must have sent you a message on the site, or through a comment on one of your topics. (For example. If you say I like chicken nuggets, and somebody says "cool" then you may get an email sometimes saying "cookiecrisp123 says cool") With your case, Jane, a user on Kidzsearch, responded to one of your posts with "hi"
Kidzsearch is absolutely safe, and nobody hacked you. If you are concerned about online safety, please feel free to talk to family or a trusted adult so they will be able to help you out.
I know that receiving such an email might have been a little frightening, but I beleive you will be okay. Have fun and keep on smiling!