The correct word would be plurality.

I sort of get what they’re saying. No other one country contributes more than 48.69%. They just said it wrong, probably.

Traffic and users are different metrics. It’s still possible that >50% of users are based in the United States, and account for ~49% of traffic. But without looking into any data, my guess would be that reddit users in the United States make up less than 50% of all users.

Both are correct. Not being a majority does not prevent the US from being the largest single nation by Reddit users.