A big thank you to everyone who left comments and answers for my previous post. The answer is passion fruit.
I did pick one with a diameter of about 4 cm off the vine and waited for it to ripen but it did not. Instead the skin started to become wrinkled so I decided to cut it open and examine its inside. I was not sure whether it was edible or not when it was unripe but I ate it anyway. As expected it was sour since it was unripe.
There are two common types of passion fruit - one that turns purple when it is ripe and the other bright yellow. I will visit the vine regularly to find out which type this one is - that is if I manage to find a ripe fruit on the vine.