I have just experienced the same: one of two jobs was set to execute at 1/1/1970 02:00 (WP-Cron) in the jobs lists.
When I clicked edit to checkt the settings in the schedule tab it was correctly set to next Friday. So I presume the script would have run correctly and that the wrong date in the list was merely a glitch.
I tried to change the time and also toggle back and forth between wp-cron and manual in the schedule tab, saving a couple of times in the process.
This seemed to solve the problem. Not sure if it was the time change or the mode change that did the trick.
(There were some ftp-deletion of a big subfolder going on in the background while all this was taking place. Perhaps this activity could also have confused the script, since I have asked BackWPup to "display folder sizes on Files tab if job is edited".)