Hello Lars
The ip host command is used to define static hostname to IP address mappings in the DNS hostname cache of the local device. This means that any time a domain name is used instead of an IP address, that mapping will be checked first, before any external DNS, if configured. This is kind of analogous to the “hosts” file found in Windows systems.
By typing the command no ip domain-lookup, you are disabling the lookup on an external DNS server, however, you are not disabling the lookup in the statically defined mappings. According to the following Cisco documentation:
In order to use this service to map domain names to IP addresses, you must specify a name server.
So a prerequisite to the mappings functioning is that a name server be specified, even if the domain lookup is disabled.
I hope this has been helpful!
Laz