It is definitely a stretch to call this a backdoor. Every security flaw ever found in Windows could have been a backdoor, and we would never have known. I think it's a bit 'tin foil hat' to try to say they are backdoors.
The flaw can be exploited if the user opens a wrong file or goes to a wrong Web site. Then the attacker can execute code as the user, who is viewing the file or Web site.