It all comes down to how the games were officiated.
In the first three games, the officials called very tight games with very little to no incidental contact allowed with lots of fouls. Lakers average 96 points per game. Advantage Lakers. Lakers win 2 of 3.
In the next two games, the officials called very loose games with loss of contact and much less fouls called. Lakers average 87.5 PPG. Advantage Celtics. Celtics win 2 in a row.
The officiating in the first three games threw the Celtics rotations into chaos. Over the last two games the C's rotations have evened out and the Celtics are playing much better playing their style of ball.