1.  While Canadians are privileged not to require a visa (passport sticky) to enter the U.S. in most cases, they still must meet the requirements for the visa category under which they are traveling.  Immigration requires a visa as do a few non-immigration categories.

2.  All persons (including Canadians) seeking the to enter the U.S. are presumed to be doing so for the purpose of immigration.  It is up to the individual to demonstrate to the satisfaction of the CBSA officer that their purpose is otherwise.

3.  The woman referred to was unable to make her case.  She was therefore considered to be seeking entry for the purpose of immigration and was correctly informed that she needed a visa.

4.  Even the possession of a valid visa does not guarantee entry.  This is why pre-clearance, if available, is desirable.  If you are denied entry, you don't need to find a way back to your country of origin.  Pre-clearance doesn't apply in this case but is used to show the reality of the border.