What domain-to-IP lookup does
The tool resolves DNS A and AAAA records available to the server resolver. A domain can return one address, multiple IPv4/IPv6 addresses, or no address at all.
Why one domain can have many IPs
Large websites commonly use CDNs, load balancing and geographically distributed infrastructure. DNS results can therefore differ by time and resolver location.
Hostname lookup is not ownership lookup
Resolving a domain tells you where DNS currently points. Use IP WHOIS/RDAP and ASN lookup when you need registration and network-operator context.