As for heart rate, no wonder it is high if 500+ W are frequently being dispensed. Given HR reacts slowly to effort (making it useless for gauging effort in short interval training sessions) it will not increase or decrease instantly when the power rises or drops, there is a delay, therefore with frequent efforts, an effort begins and ends, the body reacts and raises heart rate, this is somewhat delayed so it continues to rise beyond the duration of the effort. As such it is still rising when resting, at some point it will start to decline again, but by then another effort has arrived to push HR up, this will go on until HR near stabilises and depending on the frequency, duration and magnitude of the bursts of power, the value it stabilises around could indeed be quite high, like in the video.