I agree, they're using the term backdoor in a much wider meaning than what's usually meant. E.g. the RSA created the Clipper Chip and intentionally inserted a b

I agree, they're using the term backdoor in a much wider meaning than what's usually meant. E.g. the RSA created the Clipper Chip and intentionally inserted a backdoor to allow the government access, that's a backdoor. An attacker might use that later, but it was made by the original developer of the software with "good intentions". But TFA is using it to mean the situation where an attacker broke a window and climbed in from the outside and can now enter and leave through the hole they made.