It's actually not using the "Error" log level, but the log level named "<NO_LEVEL>", which is a built-in log level used in case of missing log level. Looking at your parser, you are, indeed, not using any log level field, hence this behavior. By default, the color and the criticality used for this level "<NO_LEVEL>" are the same as the ones used for "Error", so that if, for any reason, one log entry level couldn't be parsed correctly by a Parser which handles the log level field, this entry won't be hidden and lost in the pile of debug/info entries.
You can change the color/criticality of this level "<NO_LEVEL>" by going in the menu "Tools" > item "Options" > tab "Levels", then double-click on "<NO_LEVEL>".