Fei Daoren's original intention was indeed to lure Xi Nianmo into the historical remains. He appeared panicky so he naturally wasn't able to conceal his traces anymore.
'Fortunately', Xi Nianmo managed to find the traces of the array runes where Fei Daoren disappeared. With Xi Nianmo's God King Stage's strength, she was able to use her spiritual will to find the entrance of the array runes very quickly. With two simple array flags, she was able to open this entrance.
Xi Nianmo's spiritual will didn't sense Mo Wuji anywhere near her which was why she started to wonder if she should head in. However, she jumped right into the entrance after two seconds. She had full trust that Mo Wuji wouldn't lie to her.
Back then, Mo Wuji gave her the God Domain Nest's jade token without thinking of getting anything in return from her. This time, she wouldn't know that Mo Wuji would help her step into the God King Stage if she hadn't met him coincidentally.