Yes, I consider it an _excellent_ participation rate. A 5.5% sample size is orders of magnitude larger than that of nearly any sociological study (usually below 0.01%).
Passive users by definition agree to follow the active users' decision.
Passive users by definition agree to follow the active users' decision.
Sociological studies tend to actively seek limited size representative samples for cost reasons, and because the mathematics demonstrating the power of a limited size representative sample for making generalization about the universe from which the sample is drawn is well-known.
Comparing the size (relative to the represented universe) of a study sample actively selected to be representative with the relative size of a participant group for which there is little reason to expect it to be representative is not particularly meaningful.
Furthermore, it's been well known for the past 2 weeks that the fork was likely to happen. That means the fork was the status quo. It's what was going to happen assuming nothing derailed it.
I'm an ETH holder and I didn't vote. I was undecided and was happy enough with the decision to fork.