The worst part is they didn't read the article or failed to think about it. BBC Russia's list isn't meant to be every single Russian soldier who's died - it's the dead who have been identified in reports the journalists were able to obtain. Those who haven't been identified yet or whose deaths were noted in reports not available to journalists wouldn't be counted. 557 is the minimum possible and, as you've explained, unlikely to be the real number.
No, you drooling imbecile. A casualty is someone who has been injured and the injury caused them to become combat ineffective.
Also, the ratio of injured to dead is typically 3:1, so even 15,000 casualties would imply ~5000 dead.
The worst part is they didn't read the article or failed to think about it. BBC Russia's list isn't meant to be every single Russian soldier who's died - it's the dead who have been identified in reports the journalists were able to obtain. Those who haven't been identified yet or whose deaths were noted in reports not available to journalists wouldn't be counted. 557 is the minimum possible and, as you've explained, unlikely to be the real number.