You’re assuming that if he did tie her up, that he tied her up correctly and in a way that didn’t cause harm. Based on that description it sounds like he did become impatient or at least frustrated and then did a hurried job tying up her ankles, wrists, and then neck.
It’s worse when you realize that he ends with saying she wasn’t into it when prior to this he described making her “neigh like a horse”. Worsened then by her being “nice and tight,” which tells me she was tied in a painful and uncomfortable position (at least for an elderly woman), the pain caused her to clench, and that when Chris rammed his dick into her she was probably either screaming in pain or gasping for air…or both….