If someone unknowingly walked with a funeral procession, did he fulfill the mitzvah of accompanying the deceased?

A source-based Torah discussion of the question: If someone unknowingly walked with a funeral procession, did he fulfill the mitzvah of accompanying the deceased? This localized discovery layer presents the canonical issue for search and study without adding a new practical ruling. The author-fidelity publication clearance is preserved, while the full Hebrew source remains the controlling text for its reasoning, qualifications and conclusion.