Why does it say:

Smartmatch is experimental at /usr/bin/dnsenum line 698.
Smartmatch is experimental at /usr/bin/dnsenum line 698.

at every output?

Example:

g0tmi1k@kali-dev:~$ dnsenum
Smartmatch is experimental at /usr/bin/dnsenum line 698.
Smartmatch is experimental at /usr/bin/dnsenum line 698.
dnsenum VERSION:1.2.4
Usage: dnsenum [Options] <domain> 
[Options]:
Note: the brute force -f switch is obligatory.
GENERAL OPTIONS:
  --dnsserver   <server>
            Use this DNS server for A, NS and MX queries.
  --enum        Shortcut option equivalent to --threads 5 -s 15 -w.
  -h, --help        Print this help message.
  --noreverse       Skip the reverse lookup operations.
  --nocolor     Disable ANSIColor output.
  --private     Show and save private ips at the end of the file domain_ips.txt.
  --subfile <file>  Write all valid subdomains to this file.
  -t, --timeout <value> The tcp and udp timeout values in seconds (default: 10s).
  --threads <value> The number of threads that will perform different queries.
  -v, --verbose     Be verbose: show all the progress and all the error messages.
GOOGLE SCRAPING OPTIONS:
  -p, --pages <value>   The number of google search pages to process when scraping names, 
            the default is 5 pages, the -s switch must be specified.
  -s, --scrap <value>   The maximum number of subdomains that will be scraped from Google (default 15).
BRUTE FORCE OPTIONS:
  -f, --file <file> Read subdomains from this file to perform brute force.
  -u, --update  <a|g|r|z>
            Update the file specified with the -f switch with valid subdomains.
    a (all)     Update using all results.
    g       Update using only google scraping results.
    r       Update using only reverse lookup results.
    z       Update using only zonetransfer results.
  -r, --recursion   Recursion on subdomains, brute force all discovred subdomains that have an NS record.
WHOIS NETRANGE OPTIONS:
  -d, --delay <value>   The maximum value of seconds to wait between whois queries, the value is defined randomly, default: 3s.
  -w, --whois       Perform the whois queries on c class network ranges.
             **Warning**: this can generate very large netranges and it will take lot of time to performe reverse lookups.
REVERSE LOOKUP OPTIONS:
  -e, --exclude <regexp>
            Exclude PTR records that match the regexp expression from reverse lookup results, useful on invalid hostnames.
OUTPUT OPTIONS:
  -o --output <file>    Output in XML format. Can be imported in MagicTree (www.gremwell.com)
g0tmi1k@kali-dev:~$ 

Also does it if you do:

g0tmi1k@kali-dev:~$ dnsenum google.com
Smartmatch is experimental at /usr/bin/dnsenum line 698.
Smartmatch is experimental at /usr/bin/dnsenum line 698.
dnsenum VERSION:1.2.4

-----   google.com   -----