Formatting of YEAR values is controlled by the MySQL driver, and by default they are displayed as dates (for more information, please see https://dev.mysql.com/doc/connector-j/en/connector-j-YEAR.html).
In DbVisualizer 24.3 and onwards, you can, as a convenience, change this from the "Data Types" section in the connection properties tab.
To change this in older versions of DbVisualizer, open your connection and choose "Driver Properties" in the Properties tab. Find the property called yearIsDateType and change its value to false. Apply the changes and reconnect.
You can also to this for all connections that use the same driver by doing the same adjustment for the corresponding user driver in Tools->Driver Manager.