The "Created" date is set by the camera when a picture is taken, based on the camera's own internal clock. For a camera not connected to the Internet or GPS (like the Canon SX610), the internal clock is set by the user. There is some default starting value (different for each camera model) if the user doesn't manually set it; and the clock will drift over time (at a different rate for each individual camera). The clock can be set at any time by the user to any arbitrary date (within the date range allowed by the camera).
This is easy to verify yourself with any camera (with no GPS or Internet connection) by setting the time to sometime in the past, taking a picture, and looking at the picture's EXIF values.
The "Modified" date is set by whatever software is used to modify the picture, based on the internal clock of the device. Today, most devices (e.g. phones and computers) used to modify pictures have Internet connections and will probably have the correct time on their local clocks, disciplined from the Internet.
Both EXIF time values can be modified later without any indication (as can file creation/modification/access times).