This was my initial thinking as well. Ive seen plenty of notched logs created by modern beavers when they give up on a project.

Perhaps not even an animal. I could imagine several scenarios where a perpendicular placed log could rub back and forth across another log creating a notch over time.

I guess it comes down to tool marks on the logs notched area but the whole thing is so weathered I can't imagine that evidence is crystal clear either. Its worth noting that the other tools, which the article mentions were found at the same site, are ~100k years younger.