[Solved]-Highcharts drilldown datalabels different from parent-Highcharts

We can simply check if the point has property drilldown. So we need to change your code a little bit:

      if (this.point.drilldown) {
        return this.series.name + ", " + this.y + '%';
      } else {
        return this.series.name + ", " + this.y;
      }

Demo: https://jsfiddle.net/BlackLabel/obukypjn/