This question has been asked on this forum at least three times before:
- 19.07.4 SSH interface “unspecified” by default
- Router Access Security
- Prevent default ssh login from internet
And the answer is always "the firewall prevents access from the global Internet by default". It's a sign that there should be an FAQ on the wiki or a small note on that LuCI page to assuage these (understandable) concerns by new users. 