Does the owner lookup show a person's name?
No. RDAP lists the organization (an ISP, cloud provider or company) that received the address range from a regional registry. It contains no subscriber identity or device location, and usually not even a city. It may include the organization's public contact points, such as an abuse mailbox.
My IP is 100.64.x.x — is that a private address?
Not exactly. 100.64.0.0/10 is shared address space reserved for carrier-grade NAT (RFC 6598), used between an ISP's equipment and your router. It is not reachable from the internet, so port forwarding and self-hosting will not work with it. To see the address the outside world sees, use the 'What Is My IP' tool.
Is it a problem if reverse DNS says 'none'?
No. PTR records are set by the address holder at will, and residential lines and dynamic cloud addresses often have none. Conversely, an existing name is often a generic one from the carrier that says nothing about the service. Mail servers are the exception: many receivers reject mail from an address without reverse DNS, so those must have one.
Why is the host count of an IPv6 /64 so huge?
IPv6 uses the low 64 bits as the device identifier, so a single LAN (/64) contains 2^64 ≈ 18.4 quintillion addresses. Exhaustion is not a concern, so IPv6 is not rationed one address at a time the way IPv4 is. ISPs hand homes a /56 or /64 to use freely.