Isn't it crazy how much info those tiny stickers hold? I've been doing the same thing for years, mostly with fruits like apples and corn. Last week I saw a papaya with an 8 and put it right back. It's become a habit to scan them before buying anything.
Actually, the 8 codes for GMOs aren't really used much in stores! Most fruits and veggies still have 4-digit stickers for regular produce and 5-digit ones starting with 9 for organic. The 8-digit system was set up but it's pretty rare to see it actually on items. That papaya might have had an old sticker or a printing error.