Can vi able to modify readonly file ?

Issue

A directory has these permissions:

dr-xrwxr-x 2 UA listener 4096 Dec 19 14:13 risk/

A file in it has:

-r--rw-r-- 1 UA listener 5 Dec 19 14:42 something

listener:x:65858:mutt,jeff

Now, as user UA:

-bash-3.2$ cat risk/something  
junk

-bash-3.2$ rm risk/something  
rm: remove write-protected regular file `risk/something'? y  
rm: cannot remove `risk/something': Permission denied

as expected.

-bash-3.2$ vi risk/something

treasure  
~  
~  
~  
~  
~  
~  
"risk/something" \[Modified\]\[readonly\] line 1 of 1 --100%-- col 8

w!

"risk/something" 1L, 9C written

-bash-3.2$ cat risk/something  
treasure

vi is not a setuid program

-bash-3.2$ ls -l \`which vi\`  
-rwxr-xr-x 1 root root 632912 Jun 12  2009 /bin/vi

The filesystem is a logical volume:

/dev/mapper/sysvg-rootlv