It sounds all very speculative. I am skeptical of the idea that Matthew didn’t write Matthew in the absence of any definitive proof. Scholars often try to make their bones by these sorts of theories. Shakespeare is an example where they try to credit his work to others. This is what a friend of mine calls “a pipe and beer question”-fun to ponder and talk about but pretty fruitless in terms of increasing knowledge.
I am also skeptical about Matthew being written in Hebrew. Koine Greek or aramaic is more likely. Do you know of any early versions found that were in Hebrew?
The source Matthew was in Hebrew. The Gospel of Matthew is a different work.