BUG #14349: Parse failure (?) when LIKE swapped out for ~~

The following bug has been logged on the website:

Bug reference: 14349
Logged by: Corey Csuhta
Email address: its+postgres(at)csuhta(dot)com
PostgreSQL version: 9.5.4
Operating system: macOS
Description:

Here's this query:

SELECT 1 WHERE lower('ARTIST') LIKE '%'||'art'||'%';
Which selects:
1

But if you exchange ~~ for the LIKE statement here, Postgres does not
process it the same way:

SELECT 1 WHERE lower('ARTIST') ~~ '%'||'art'||'%';
Returns the error:
argument of WHERE must be type boolean, not type text
LINE 1: SELECT 1 WHERE lower('ARTIST') ~~ '%'||'art'||'%'

Is this expected? The documentation implies you can swap these operators and
get the same results.

I believe I have a minimum example above, the swap works if you do not use
|| or if you wrap the left and right side of the expression in parenthesis
to help the parser.