I'm assuming that on the non-flash shot, your flash had not fully recharged, and so you got a shot without?
I have been in situations like that, and sometimes, it's really nice to see the flash version and the non-flash version to compare just like yours above.
In one situation, I realized that NOT using the flash was better. I was shooting a jazz club with really sh*tty lighting. My flash batteries started to die, and I forgot my replacements.
I really couldn't tell any advantage to not using flash with the LCD. But when I got home, I started processing. I was happily surprised to see that non-flash photos were better in that situation! My ISO's were skyrocketing, but I took them into Black and White, and the grainy qualities looked fine.