No joke. The original ad is screen captured and can be seen at the link. Note: The ad has since been updated to simply "DOE". In addition, they even managed to misspell "compensation".
"Seattle-based group The Freedom Socialist Party, which owns socialism.com and regularly campaigns for a $15/hour minimum wage, advertised a job on Wednesday that offers just $13 an hour.
The group has taken particular interest in campaigning for a higher minimum wage in Seattle, where the posted job is located.
The advertised job’s Indeed.com [linked] description says that the wage is negotiable depending on experience, but the group has said that living wage must start at at least $15–not $13 or $14 an hour."