Seems like it would be an easy thing to confirm. You'd think Immigration would have more important and pressing matters than a French citizen on vacation in BC accidentally jogging over a border like that. In this day and age, to take two weeks? Surely they knew exactly what the situation was in about two hours.
Reminds me of a story my parents used to tell us. We used to drive down to North Dakota all the time when I was very young. One weekend, my grandparents decided to come along, in their own car. My grandfather had never driven over the border before, made a wrong turn somewhere and ended up just driving over the border. He was pursued by numerous law enforcement vehicles, pulled over and was surprised to learn he was essentially lost at the border. They all had a good laugh and let him go. What if that happened today?