Actually that was a mid-match change in tactics by Novak - probably pre-planned. In the first set, he hit very aggressively from side to side and in particular hit very big to force errors from Medvedev’s FH. In the last game of the 1st set, he also hit very flat and lower over the net than usual to take Medvedev’s time away to get the decisive break.
Then, when Medvedev seemed to be adjusting and hitting better FHs himself early in the second set, Djokovic switched it up and started hitting more conservatively to the middle of the court slightly to the BH side, but still with enough depth where Med couldn’t hurt him. Med then got impatient during his service games and tried to finish points quicker and this led to a whole bunch of unforced errors which unhinged him mentally, broke his concentration and confidence - the match was essentially over at that point as he mentally gave up.
So, Djokovic gave a masterclass in how a champion can have different tactics to pace himself during a match and force his opponent to adjust - in most cases, the opponents don’t have the skill or mental calmness to adjust as they are constantly feeling pressured by the deep returns and shots hit by Novak from close to the baseline. One wonders what other tactics Novak had pre-planned if the match went to four or five sets.