Welcome to Android Central! Which phone? This happens from time to time (especially with the more obscure manufacturers). The system app probably just didn't have the correct information added to the filename. I wouldn't worry about it.
Happens quite often. Android doesn't have a monopoly on this. It's more a coding issue. Why change the date if it isn't critical to operation. Why 1969 is one of the defaults I've never heard a reasonable answer.
The 1969 is an easy explanation.
A missing date gets the value of zero. The "zero" date for Android and Unix is Jan 1, 1970. When adjusted for a time zone west of GMT, you get Dec 31, 1969.