Maybe he means that someone who has true Yiras Shamayim will have good middos by definition.
Even if that’s true, it still makes sense to look out more for good middos because it is much harder (if not impossible) to tell if someone has Yiras Shamayim than if they have good middos.
Also, even if in theory, Yiras Shamayim should include middos tovos, I’m not sure if it is necessarily the case l’maaseh. I think that most of the time when Frum people lack good middos it is either because of emotional issues or because of bad chinuch, and having yiras Shamayim doesn’t necessarily help. If someone naturally has a bad middah, it is very, very difficult to change it even with all the Yiras Shamayim in the world.
While I do think that middos tovos is the most important quality to look for in a spouse, I think that one should look for both middos tovos and Yiras Shamayim. If someone has midos Tovos but is lacking Yiras Shamayim, then their middos tovos may be somewhat superficial and they may change if circumstances change. I think that Yiras Shamayim provides a good basis for the middos tovos and ensures that they are likely to stay.
Also, it seems to me that if the person has good middos but you don’t share common goals, there is a danger that the marriage might not last when there are difficulties. But if you share common goals (meaning, you are both true Ovdei Hashem who got married l’sheim Shamayim), the marriage has more of a foundation and is more likely to withstand difficulties.
So bottom-line, I think that good middos are more important, but it is important to have both.