The "Domain Name" DHCP option 15 is sometimes used to carry a list of domains instead of just one. In such a case it seems to be a common practice to use the list verbatim as a "search" list (e.g., in resolv.conf). While the NetworkManager seems to try to do it's best to cope with the situation in nm-dhcp-systemd.c/lease_to_ip4_config(...):

[...]
        /* Domain Name */
        r = sd_dhcp_lease_get_domainname (lease, &str);
        if (r == 0) {
                /* Multiple domains sometimes stuffed into the option */
                char **domains = g_strsplit (str, " ", 0);
                char **s;
                 
                for (s = domains; *s; s++) {
[...]

, systemd counters by doing it's best to break the things down by returning an "escaped" string out of the sd_dhcp_lease_get_domainname(...). So if you happen to have your DHCP set up to return "mycompany.de mycompany.cz mycompany.com" in the Domain Name field, systemd turns it into "mycompany.de\032mycompany.cz\032mycompany.com" which obviously passes the parser logic intact and gets later used as a domain name.