The article does say that it is only speculation that the dam is broken by the stranger opening its solar sails, but if you plant your scout on the dam you can see it stays at 100% integrity until the stranger begins to move, and it takes like 15% damage when it does. So I'd say more than speculation, but am curious to see what others might say.
I know the ships log defines the stranger as a ringworld, but it isn't one. ringworlds encompass an entire orbital plane. the stranger is an O'Neil cylinder, albeit a very squished one.