You saw a meaning given by a disreputable website or book, written by someone with more imagination than research skills or scruples.
Edward is very straightforward, it's Old English, composed of the elements 'ead' meaning 'prosperity, wealth; happiness, bliss' and 'weard' meaning 'guard'.
Edward has survived from before the Conquest to the present day with uninterupted use and been exported to a variety of languages, unlike most Old English names.
Sorry to disappoint but there's nothing about mists in your name. It's dimly possible that the meaning you found was copied (extremely common, out of all the books and websites on names out there, 95% are pure copies of other sites - lots of enthusiasts/fans, very few researchers or linguists) from someone with a *little* knowledge of Old English who confused the 'ead' element with 'ea' meaning 'river, stream'...how they would explain that rogue D in there between ea and weard would be a fun question to ask them though ;o)