C++ new operator with std::move to "copy" pointer

I recently find a code snippet as follows:

  // To be specific: the "Item" can be viewed as "std::pair<xxx, xxx>*" here
  void moveItemDuringRehash(Item* itemAddr, Item& src) {
    // This is basically *itemAddr = src; src = nullptr, but allowing
    // for fancy pointers.
    // TODO(T31574848): clean up assume-s used to optimize placement new
    assume(itemAddr != nullptr);
    new (itemAddr) Item{std::move(src)};
    src = nullptr;
    src.~Item();
  }

The code is originated from the Folly Lib of Facebook. The functionality of this code is simple: copy std::pair* referenced by src to the memory pointed by itemAddr.

The implementation should be very simple, as mentioned in the comment. But actually, the code does not. The new operator with std::move is confusing, and I am not sure what is happening under the hood. I guess. Item{std::move(src)} construct a temp object with move ctor of std::pair*. And the temp object is copy to the object pointed by itemAddr by copy ctor of std::pair*. I am not sure if my guess is correct. Thank you for sharing your opinion. By the way, I was wondering if there is any performance benefit from this new operator with std::move.

Another question is why src.~Item() is needed? For safety, I need to set src (std::pair*) to nullptr. But why I need to use src.~Item() to dtor a nullptr?