I don't know the specifics of finches but these are options I could guess for any bird getting out:
-Forgot to put bird away before
-Someone else let it out while you were gone (perhaps by accident)
-Bird slipped out while you were putting it away and didn't notice
-Guillotine cage doors (would close itself)
-Squeezed through cage bars (esp on wire cage)
-Cage door was left open/unlocked, bird got out and accidentally closed door coming out
-Food bowl doors could have been compromised
I discussed how Kili used to get out and how I put clips on the cage doors to prevent that:
posting.php?mode=reply&f=7&t=522Kathleen and I were at a birdstore recently and were watching a macaw on the verge of escaping its cage because it managed to get its beak out and flipped the gravity flap on the food doors and was about to get the door open. We closed it just in time or they would have had an out macaw.
EVERY SINGLE cage door for any bird cage should have at least 2 independent latches. The gravity flaps are fine but another latch is a must. Kili's main cage door is quite secure with a gravity flap at the top and a bolt latch in the middle. They are far apart and pretty much impossible to reach. There is no way the bird is getting out that way. So instead, it focuses all its attention on the food doors where there is only a single latch that is easily manipulated. This is why I added extra clips to it and so far so good.