Trouble with: setAdvertising heart_rate

Quick update, I've got the heart_rate service advertising and "working". Note that I lifted the setAdvertising values from here and just copied the GAPSETADVDATA value into a hex array, but I really don't understand why it works.

var hr = 65;

function update() {
  hr++;
  if (hr > 120) {
    hr = 65;
  }
  
  NRF.updateServices({
    0x180D: { // heart_rate
      0x2A37: { // heart_rate_measurement
        notify: true,
        value : [0x06, hr],
      }
    }
  });
  
  setTimeout(update, 1000);
}

NRF.setServices({
  0x180D: { // heart_rate
    0x2A37: { // heart_rate_measurement
      notify: true,
      value : [0x06, hr],
    },
    0x2A38: {
      readable: true,
      value: [0x02]
    }
  }
});


NRF.setAdvertising([
  0x02,
  0x01,
  0x06,
  0x05,
  0x02,
  0x0d,
  0x18,
  0x0a,
  0x18
], {
  name: "puck heart", // this doesn't stick at all, no idea why
  showName: true,
  discoverable: true,
  interval: 600
});

// if I update too early, it seems like GATT is still trying to do the previous updates
setTimeout(update, 2000);