Outside of the division, the Lakers had a better record than the Grizzlies

In the Western Conference playoffs, 5 of the 8 teams were from the Pacific Division. The remaining 3 teams were split between the Western Division (Nuggets, Timberwolves) and the Southwest Division (Grizzlies). During the regular season, each team plays 4 games agains their divisions rivals for 16/82 games being against the division. The 5 playoff teams in the Pacific beat up on each other while the Grizzlies dominated the Southwest against non-playoff caliber teams. If you look at the conference and overall records of the Grizzlies vs. the Lakers outside of their respective divisions you see very comparable records:

The West had so much parity this year.