It is close, but it is not the lowest, there is only 5 episodes with an average score lower than 6:
S06E08 5.38
S05E06 5.40
S06E01 5.60 S08E04 5.65
S07E06 5.71
Oddly enough there is also only 5 episodes with an average score higher than 9:
S02E09 9.53
S03E09 9.25
S03E04 9.23
S01E10 9.14
S01E08 9.03