If you pass a timestamp as a string (which is how it would come out of the DB) instead of an int, you get different results:

core_date::strftime('%c', '1708405742'); --> 28 February 5742 at 5:08 pm
core_date::strftime('%c', 1708405742);   --> 20 February 2024 at 5:09 am

While depricated in 8.1 and up, strftime gives a very different (and more expected) result:

strftime('%c', '1708405742'); --> Tue 20 Feb 05:09:02 2024
strftime('%c', 1708405742);   --> Tue 20 Feb 05:09:02 2024 

I also just noticed the format is different, but I was mostly concerned about the actual date/time being parsed incorrect.

I know this is barely used in core (I think date_format_string() is the only thing that directly uses it), and there is a separate ticket to depreciate strftime (MDL-77366) in core completely, but I figured I should at least raise this for others who might run across it.