There likely was a great deal of this at some point before 2015, but in 2015 BC finally started tracking who was buying homes and brought in a foreign buyer tax and since there there's been only ever more scrutiny on foreign buying, and from everything I've read foreign buying has fallen off a cliff.
Because there was no data tracked before 2015, whether or not there was indeed a significant amount of foreign buying remains speculation and theory but there are some signs that support the notion that it was important.
For example major luxury condo builder Westbank has significantly reduced their operations in Vancouver, pivoting away from super luxury homes explicitly marketed as pied-a-terres and in the pages of Monocle magazine and are now building increasingly in the USA and even Japan. Some of their projects in Vancouver changed from being condos to rental. That this all happened post foreign buyer tax suggests that foreign buyers were a critical part of their business plan and they needed to remarkably change it after foreign buyers went away.