רש"י explains מתגלגל that the בהמה rolled the food from the רה"י to the רה"ר and the query is whether we follow the taking and he is חייב or we follow the eating and he is פטור.
However, תוספות explains מתגלגל that it rolled on its own and the בהמה stopped its progress and ate in the רה"י. The query is whether we follow its destination and he is פטור. Or we follow the place where he stopped and ate it and he is חייב.
It is a case where this one is not benefiting, and this one is not losing - זה אין נהנה וזה אין חסר הוא
The dweller is exempt from paying even if it is a חצר דקיימא לאגרא as long as he is a גברא דלא עביד למיגר. Preventing someone from using his own property is considered a גרמא for which one is not liable.