When the AUTO_CD option is set, and the first input word is a parameter...

• Parameters with a value of a directory are highlighted by ZSH_HIGHLIGHT_STYLES[autodirectory]
• However, the HOME parameter is highlighted by ZSH_HIGHLIGHT_STYLES[unknown-token]

I expected HOME to have the same syntax highlighting as other parameters with a directory value (e.g. PWD, OLD_PWD, etc.).

Is this the same for everyone else?

The attribute of HOME is a scalar-export-special, (see echo $parameters[HOME]).