I do believe that fact-checking and identifying clickbait is important, but in this case I think you are nitpicking with no cause and adding no substance to the discussion.

The article mentions a sum of 6,751 deaths not including several countries (Philippines and Kenya), so "at least 6,500" is correct. The article also says "While death records are not categorised by occupation or place of work, it is likely many workers who have died were employed on these World Cup infrastructure projects", so the "constructing stadia for the World Cup", although a bit loosely, is also true.

I don't get what you were trying to open our eyes to with your comment. Even if only 1,000 workers were confirmed to be deaths directly related to building stadia it is just as horrible and needs to be known.