What is BIP32-style derivation? I am reading the technical "specification" for stealth addresses, available here. The core idea is described in the following paragraph:


  Using Elliptic curve Diffie-Hellman (ECDH) we can generate a shared
  secret that the payee can use to recover their funds. Let the payee
  have keypair Q=dG. The payor generates nonce keypair P=eG and uses
  ECDH to arrive at shared secret c=H(eQ)=H(dP). This secret could be
  used to derive a ECC secret key, and from that a scriptPubKey, however
  that would allow both payor and payee the ability to spend the funds.
  So instead we use BIP32-style derivation to create Q'=(Q+c)G and
  associated scriptPubKey.


I understand everything except the last sentence. As far as I can tell, Q and c are known to the payee and payer so the keypair Q'=(Q+c)G is also known to both. How does Q' allow for only the payee to spend the funds? How does BIP32-style derivation work?
I believe there is a typo. It should instead read Q'=(d+c)G=Q+cG. The private part d+c is an offset of the payee's private part d, so only known to the payee. The public part is an offset cG, known to both.