What to do about Lumen Gentium 16?

I continue today my reflection on Islam that has been prompted by an email I received from a friend. In that email he brings up the Vatican II document Lumen Gentium, §16, which in part states:

But the plan of salvation also includes those who acknowledge the Creator. In the first place amongst these there are the Muslims, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge mankind. Nor is God far distant from those who in shadows and images seek the unknown God, for it is He who gives to all men life and breath and all things, and as Saviour wills that all men be saved.

The part I am struggling with here is “the plan of salvation also includes…the Muslims”. Without explaining what is meant by “the plan of salvation” the document makes it sound like (at least to me) that all religions are valid paths to salvation. (The idea that all religions are valid paths to God makes me apprehensive and defensive, which in turn can lead to quick tempered reactions on my part. But, such reactions can obviously be counterproductive, which I will address later in this series.) But of course this couldn’t be true because it contradicts what the Church has always taught: that salvation comes to us only through Jesus Christ.

In order to try and resolve the problem of the meaning of “plan of salvation” I tried searching for a commentary on Lumen Gentium. There was only one document that appeared useful, which was by Daniel J. Castellano. And, to make sure the interpretation given to the phrase in question was valid, I tried looking up the author. I couldn't find much information but it does seem that he is very intelligent Catholic (undergrad from MIT, graduate studies at Boston University). Hopefully that means his interpretation can be trusted because I have not found anything to corroborate what he says. Below is what he has to say about the phrase in question (rest of the article here):

Since God’s “plan of salvation” is implemented solely through the Church, the Council is here asserting that the Church is linked in some way to all who believe in the Creator. This is most obviously the case with the Muslims, who share our belief in the one God of Abraham. It cannot be said that the God of Islam is another false god, even if the Muslims might differ from Christians in theological doctrines. They clearly give honor to the Creator, not a mere creature, and respect His sovereignty over all men. This ability to recognize the one God is a gift of the Holy Spirit administered through the Church. Going further, St. Paul famously commended the Athenians for honoring a mere “unknown God.” (Acts 17:23) Though they had no positive understanding of the one God as the Muslims do, they at least had the inclination to honor that which transcended their understanding of creation. This seeking is also a gift of the Holy Ghost to the Church. We should not be surprised to see this salvific activity beyond the visible structure of the Church, given the Savior’s desire for all men to be saved. (1 Tim. 2:4)

If this interpretation is accurate we could therefore say that the “plan of salvation” is simply God’s desire for all mankind to be saved, which is true and therefore, “plan of salvation” does not somehow make Islam, or any other religion, equal to the one and only true religion established by Jesus Christ.