The huge majority of applications with any c++ code have some sort of memory safety vulnerability. Codecs are a classic place where this shows up all the time. Why would this vuln out of the literally gazillions of similar vulns be considered a backdoor?

Never attribute to malice that which can be adequately explained by stupidity. So - yes, possible in theory, but quite unlikely.

"Never" seems a bit much, if you accept the premise that all backdoors would be made to look like accidential security flaws.

But since there are probably a lot more accidential security flaws than backdoors, I agree that erring on the side of stupidity is justified.