No. He still needs the PIN to actually use the Sign-Key. However that can be key-logged if your computer is compromised, so the extra 'touch' does add quite a b

No. He still needs the PIN to actually use the Sign-Key. However that can be key-logged if your computer is compromised, so the extra 'touch' does add quite a bit of security. The U2F needs touch by definition anyway. GPG/PIV do not, this capability was added with the Yubikey 4.