No, it's not. It's an entirely separate class of service per the tariff, and the presence of the word "economy" is irrelevant.

Under APPR, there's no compensation owing for a downgrade, but there is a requirement to refund the difference in fare. Of course, AC, like every airline, tends to calculate that in a very unfair way, and is likely to offer very little.

So yes, asking to be re-booked on a flight that does have PY is the best option.