Okay I must admit, I just also messed up left and right.
But also Apple does…At least in German even the light grey info text above the options in the "swipe right" menu is wrong. It says there would be options to delete, mark and archive messages when swiping right, which obviously are only available for left swipes…
Either way, the problem persists, if I do a long left swipe emails get deleted/moved to trash immediately. Instead I would just say same result as for a short left swipe. For me there really is the two step verification missing for such a strong action. (Even if a mail gets only moved to trash, I still need to go there by several steps and move it back manually to the inbox.)
What are your settings for the following (out of curiosity):
Settings > Mail, Contacts, Calendars > Swipe Options > Swipe Right:
and
Settings > Mail, Contacts, Calendars > (mail account you are using) > Account > Advanced > Move Discarded Messages Into:
For swipe left I have added the mark email button.
Emails are moved to my Deleted Messages folder when deleted. (That's perfect, don't wanna change that, just the way to "delete" message feels too dangerous and easy going for me… I so often move emails to trash when I just want to mark them for being important or sorting them away.)