"Man sagte mir, dass Sie ein Herz hätten."
Agreed. We'll work on making sure the sentences in the skills aren't too hard (and are more relevant to the skill they should teach). In case anyone's still curious: "hatten" would change the meaning to something like "...that you used to have a heart (in the past)" whereas "hätten" is used here because we are told something and don't know it for sure. Definitely too abstract for this skill though, thanks for reporting!
Here the meaning is "They told me you had a heart" or "People told me you had a heart" or "I was told you had a heart". "You told me that you had a heart" has another meaning.
Although "man" has no straight equivalent in English and can be translated as "one" or "they" or "people" or "we" or even "you", the translation depends on the context, you can't blindly use one of them in all the cases.