Still not a majority.

If you add the eligible voters who chose not to vote (indicating they were fine with whoever wins), then it's a clear majority. If you don't vote, your vote is effectively for the winner.

That makes zero sense at all. They didn't know who would win in advance.

But they were OK with that person winning, whoever it would be. If they weren't, they would have voted for someone else.

That's not how a majority works. You're also making assumptions about why they didn't vote.

not being motivated enough to vote against != support in terms of claiming a popular mandate. If I just don't care who wins, you can't say I support either candidate.

At most you could say my inaction prevented the winner from losing I guess.