Yeah, costs estimates under Obamacare have been revised downward. Cost estimates during Bushes term were revised upward.
Here's what you missed or ignored from the same article,
“When the CBO goes back and revises their baseline, historically they’ve adjusted upwards,” said Tricia Neuman, director of the Kaiser Family Foundation’s Program on Medicare Policy. “So the fact that there’s been year-after-year downward adjustments is fairly remarkable since they occurred after the ACA” was signed into law.