Why status code 500 for errors in user supplied health checks?

[trasch]

I'm playing with health checks currently, and tried this code (from the README):

var strata = tilestrata({
    healthy: function(callback) {
        callback(new Error('CPU is too high'), {loadavg: 3});
    }
});

This returns an HTTP code 500, which I would expect only if my request crashed the server. Also, the returned JSON already includes a hint that something is wrong ("ok":false).
I wonder, what was the reasoning to set the status code to 500?