That happened to us once, not quite as similar, but my husband had left the back gate WIDE open and I let Belle out the back. A few minutes later I was calling for her, no Belle. I thought she was snooping behind the shed (as she often does) so I went out and looked, the gate was open and i panicked. I called and whistled, yelled at my husband for leaving the gate open, etc. etc. We went to the front garden, there she was, grazing on the grass, not a clue as to what was happening, phew.
It's great you have nice neighbours alright, she's safe now.
Desrae, guardian of two tri-coloured cavaliers, Belle 3 years old and Bobby 1 year/8 months.