Yes to the file question (the update post hook is working in the same file).
Regarding the other question, there are definitely ACF fields in the page that I’m updating. However, interestingly enough, if I try to error_log the $_REQUEST or $_POST arrays in the post_updated
hook I have set up, all I get is something like user_locale.
Hey, late response, but try this:
$text_area = get_field("text_area");
$text_area_arr = explode("\n", $text_area);
$text_area_arr = array_map('trim', $text_area_arr);
If you put each value on a new line in the text area, then $text_area_arr should be an array with each new line value. array_map is to get rid of extra white space.