Yes, it was an ambush.
Even a Semi-Saint stooped to ambush Qin Changqing, a Great Luo, what befitting behavior of an Evil Immortal.
Moreover, these guys were not easy to shake off.
Right now, the Moon Goddess was still expelling toxins from her body. Although these toxins weren't difficult to drive out, after being poisoned, she had gone all out, which caused her to be afflicted more deeply.
Therefore, the Moon Goddess needed some time to completely detoxify.
The Evil Sword Immortal had anticipated this, thus launching the ambush to exhaust the Dao source that Qin Changqing had acquired.
After all, a Pseudo-Saint is not a Semi-Saint.
Once a Great Luo comprehends the Dao, the obtained Dao source is limited; once it runs out, they can't access Pseudo-Saint Power anymore.
The best place to replenish Dao source is in the Immortal World. It's not that it can't be done in the Outer Heaven Realm, but the risk is more than a hundred times greater.