We can't know what they want if they don't or can't vote. Putting "they voted yes" in their mouth sounds insulting to me, but I'm an outsider to the UK so maybe it's wrong for me to say that
Yes, of course, they didn’t give a shit. They couldn’t be bothered. Outcome was whatever for them.
You could also just say they didn't exist if it makes you feel better. But calculating the percentage from the eligible voters gets you no where. They didn't vote. It just makes the number smaller. Whatever. It doesn't change anything. It's not first to 50% of eligible votes. It's the majority of voters.
But I am angry at everyone who doesn't vote if they can. Especially if they complain that this isn't what they wanted.