They’re not praying to the Holy Trinity, Father, Son and Holy Ghost; so, “No”, they are not praying to the One True God. Neither are the Jews.
Lumen Gentium is just plain wrong in this regard.
We can judge objective observable things ("That man says he does not believe Jesus is the Son of God") --- We do not read souls. That's why neither of us will be the Judge of Souls. Thank God.
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