Apparently it's just a cool story but not true. "This tree is often referred to as the “upside-down tree” by students, as its branches resemble roots. The reason for the unusual shape comes from its cultivation method: rather than sprouting from a seed, this tree grows from a Camperdown elm cutting that’s grafted onto the trunk of a Wych elm."
http://web.archive.org/web/20161101060819/http://old.ubyssey.ca/culture/discover-the-best-trees-on-campus-992/
http://web.archive.org/web/20161101060819/http://old.ubyssey.ca/culture/discover-the-best-trees-on-campus-992/