It's because the heirloom is a pIN which is matching "in" much earlier than you want so the entire first group is "that an unfortunate citizen lost after being attacked by a lesser griffin in Griffin's Keen"
This is a great website to use when you're having trouble with a regex: https://rubular.com/
Just enter your regex and the line you are matching and it will show you if it is matching correctly and which groups are being matched and all that good stuff.