Override typo in multiple parent theme files?

You can override it, but you’ll have to create Child-Theme versions of archive.php, attachment.php, and single.php.

Since it’s a translation string, you might be able to do something hackish, like provide a en_US.MO file that translates “Filled under” as “Filed under” (or whatever you want). But that gets tricky – and This Theme appears to be _doing_it_wrong(), putting HTML tags inside of __(). So I’m not sure I’d even want to start messing with translation files.

The best solution would be to report the incorrect string as a bug, directly to the developer.