I'm guessing you took advantage of the fact that you move forward slightly with each swing of a weapon or scythe. There's a few places where you can get out of bounds that way, if I recall correctly.
You can get into the secret woods without upgrading the axe by placing a chair in the right spot. There's a discussion of it in the Morel Moroseness thread.
Not sure if the weapon thing works to get out (I'm guessing it doesn't, since you posted this), but the chair thing does work in reverse - just stand where you would put the chair to get in, and put the chair where you would have stood on the outside of the log.