it's a red (ha) herring? Sounds like something they said to keep us watching. Apparently the series finale is full of twists, maybe Jason not being the Gargoyle King is the twist
I love how normal this bull**** is to Jughead and Betty. They're just like "only one way to be sure it's Jason. dig him up
" rather than thinking "well he's dead so she's clearly bull****ting"