You are still advertising IPv6 reachability information (TLVs #232 or #236). You can disable it
set protocols isis no-ipv6-routing
Or I think that you could do the opposite which is to allow only IPv6 (and although the "main" topology is non-existing)
If you enable multi topology TLVs #229 I think you should see IPv6 routing information
set protocols isis topologies ipv6-unicast
Let me know if it worked.