Heavenly Emperor Yu Siang not only dragged Shangguan Linlang and Shangguan Qingchen's grandfather, Shangguan Qingtian, into the mix, but he also implicated the Greek Celestial Court and the Nordic Pantheon.
Yu Siang's thinking was straightforward: Why should the Eastern Celestial Court be the only 'victims'?
The past war between gods and demons aside for the moment.
However, the incidents related to the Yulong Dynasty and the disappearances of Shangguan Haotian and Xiang Wan, were all connected to the Greek and Nordic Pantheons as well. Since Shangguan Linlang had now 'returned in full force' to settle matters with them, it was only fair to drag their little friends into it too.
Otherwise, the Eastern Celestial Court would be at a disadvantage.
Furthermore, Yu Siang actually wanted to subtly remind Shangguan Linlang that opposing the Divine Race would not be easy. At the very least, the number of 'enemies' was quite significant.