No, the error is talking about MySql.Data.dll, not your version of the database. Did you get the files from the mojopoportal-2-2-6-8-mysqldatalayer.zip?
In medium trust its probably using the MySql.Data.dll from the GAC that was installed by the host and that one may not be the expected version.
If it were me I'd stay away from trying to use MySql in Medium Trust and use MS SQL instead or move to full trust hosting.
Best,
Joe