PPG analysis beyond HR at rest

I modified the test code a bit, and it seems that the HRM event always gets a higher BPM than the manual counting:

var M = g.getWidth() / 2;
var yr, yg, yc, yd;
let beats = [];
Bangle.on("HRM-raw", (hrm) => {
  g.scroll(0, 1);
  g.setPixel(M, 0, "#ff0");
  g.setColor(hrm.adjusted ? "#000" : "#0F0").fillRect(
    yg,
    0,
    (yg = hrm.raw / 32),
    0
  );
  g.setColor("#F00").fillRect(yr, 0, (yr = M + hrm.filt / 256 - 30), 0);
  g.setColor("#F0F").fillRect(yc, 0, (yc = M + (hrm.raw - hrm.avg) / 128 + 30), 0);
  if (hrm.isBeat) {
    g.fillRect(yr - 4, 0, yr + 4, 0);
    beats.push(Date.now());
  }
});
Bangle.setHRMPower(1);
Bangle.setLCDTimeout(0);
Bangle.setLCDPower(1);
setInterval(() => {
  beats = beats.filter(b => b > Date.now() - 60 * 1000);
  console.log(beats.length, "BPM");
}, 1000);
Bangle.on("HRM", (hrm) => console.log("OFFICIAL:", hrm.bpm, "BPM", hrm.confidence));

Any idea why?