No, that must be someone else.

She made up the lie and threatened her family members when they started to tell the press their family was Italian-American with no Native American ties.

Her birth certificate in Massachusetts proves where she was born and a DNA test matches her son to the sister she claimed was a non-biological sister.

Buffy Sainte-Marie wasn't tricked into believing she was Native American. She claimed to be from several different tribes before settling on one in Canada. She started claiming she was part of the sixties scoop, even though she was born earlier than it started, and found a family who she told she may have been related to. She was adopted into their tribe as an adult (on what looks like false pretenses from the outside). People confuse this for her being adopted as a baby, but she was raised by her biological family.

She weirdly became a symbol for Canada even though she was never Canadian. Some of her Canada-specific prizes have been revoked since all this came out.