I think fans are pretty good at spotting the difference between their team losing badly because they are having poor luck, poor decision making, or are just not good enough, and their team losing badly because their attitude is poor. All of the first conditions may have applied to the Eels, but their attitude was very bad and they deserved the booing.
I used to think leaving early was crazy, just because you might miss something good, even if your team is down by 50. But now with a baby I take to many games, if it is hot or wet or cold, or my boy is just cranky, I would leave early if the game result is decided.
Fans pay their money, they can boo or cheer and stay or go as they please.