The poem tells of a very talented but poor girl who wants to wear a proper dress but can only make wedding robes for other rich families. The same as Xu Ling, who feels bitter to have no opportunity to show his talent due to his social status. The phrase basically says Xu Ling was still unsure before which powerful party he was siding with by investigating.

https://www.northwestflower.net/sha-po-lang/book-2/chapter-11-rising-wind/11-iii

Before, much like everyone else, Master Xu placed an irrational trust in the Marquis of Order, the representation of the Black Iron Camp. It seemed that as long as there was Gu Yun, they could charge ahead whether it be a dragon’s cave or a tiger’s den, if the sky fell, he would be there to shoulder it. Of course, that trust was now shattered.

Deputy Inspector Xu's handsome face was pale blue, he still held onto the last line of hope and asked, "Marshal… is it also your intention to cross the river?"

"How is that possible?" Gu Yun looked at him with his gaze filled with confusion and said, "Tch, I already told Master Feng Han long ago that this thing is certainly not reliable. The reason why the Black Eagle can fly fast is that it relies on human control when it reaches the sky. He made such a large thing, it's alright in calm weather, in the face of a little storm and rain, it instantly comes down. Is it not to hand our lives to the enemy on the battlefield? You see, it's already done for."

Ge Chen threw up until his internal organs were turned upside down and his tears were running: "I will... definitely tell Master Feng Han after returning."

Xu Ling's liver almost busted from fright. He could not be as optimistic as Ge Ling Shu, feeling that he could never return again.

Fortunately, someone could still speak human language; Chang Geng turned to Deputy Inspector Xu and said with a laugh, "Don't listen to him, he was only scaring you. This place is flat, there are no enemy camps in sight. It shows that the enemy's leading force is not nearby at all. Tonight, there are also thunderstorms and rain, the sound of the explosion and thunder would have blended in together. He has calculated already, it won't attract a large number of people, at best, there will only be some patrol officers coming to check."

Gu Yun revealed an evil smile.

Xu Ling looked at Yan Wang with tears in his eyes. His Highness's courage and intellect that remained unfazed even in the face of danger were already enough for him to bow down in respect. At the moment, he sincerely said, "Yan Wang is wise."

"Not at all," Chang Geng waved his hand. "Being fooled by him since childhood, I soon learned my lesson."

Xu Ling: "..."