Hello Christian
The ip igmp snooping querier command is used to enable the querier function on the local switch. The command does allow you to specify an IP address, but only for the purpose of choosing the source IP address of the querier, again, on the local switch. Note that the IP address you specify must be an IP address on the local device. If you specify the IP address of the c9300 switch, you are not telling the local switch to use the c9300 as the querier. If that address is not found on the local device (which in your case it is not), then it will use the following process, as described in this Cisco documentation, to determine the source IP address of the querier:
When enabled, the IGMP snooping querier uses the IP address as the query source address.
If there is no IP address configured on the VLAN interface, the IGMP snooping querier tries to use the configured global IP address for the IGMP querier. If there is no global IP address specified, the IGMP querier tries to use the VLAN switch virtual interface (SVI) IP address (if one exists). If there is no SVI IP address, the device uses the first available IP address configured on the device. The first IP address available appears in the output of the
show ip interfaceprivileged EXEC command.
If you use the show ip igmp snooping querier command as shown in this Cisco documentation, you will be able to verify that the IGMP querier has indeed been enabled on the c1000, and it is likely that the IP address it has chosen to use is lower than the one used by the c9300, so it is becoming the querier. To resolve the issue, disable the querier functionality on the c1000 using the no igmp snooping querier command.
I hope this has been helpful!
Laz