while isn't IO::Handle anywhere, and duplicates the FileHandle shown in the original code

It's an object of type IO::Handle, as shown in the first line of the dump. Basically IO::Handle->new boils down to blessing a new symbol as returned by Symbol::gensym (which explains the second line of the dump) into the class IO::Handle (source). If you step through the code, you should see the following:

**Before** the open()
0  IO::Handle=GLOB(0x1948fb2)
   -> *Symbol::GEN0

**After** the open()
0  IO::Handle=GLOB(0x1948fb2)
   -> *Symbol::GEN0
         FileHandle({*Symbol::GEN0}) => fileno(7)
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So the FileHandle appears to be the result of opening the file.