Wort storing - acidental sour. Repeatable?

So a while ago, I learned about partigyle brewing, and decided to give it a go and make a barleywine and then sparge for a smaller beer like a mild or something.

well, brew day didn't go to plan, and I wound up with a sanitized bucket of un-boiled, pretty low SG wort, that i just didn't have it in me to continue working with. So, I decided to cap it, and finish it the next day, knowing that if it developed some lactic character, I was fine with that.

Well, that didn't work out either, and so long story short, it sat for 3-4 days at room temp.

When i finally got to it, i thought it would be a nasty mess, but i was greeted with a nice tart, fruity smell upon opening it, and so i decided to boil it as i had planned.

That was about a month ago. I snuck my first taste last night, and it was quite good. I think i could improve on it too, and make it even better. (more sourness would be nice i think).

So the question is, did i just get really lucky? Or do you think i could repeat this process and get a same or similar result?

It would be very convenient. I'm planning on making barleywine at least once a year, and if i can rinse for a smaller beer that i don't have to boil immediately, and even better, one that will be nice and sour, i'd be very happy.

I was thinking about possibly developing a no-boil beer, kind of like an english/american spin on a berliner-weisse that i could make whenever i do a BW. What i have is close. It's thin and tart, with a nearly imperceptible amount of hop (fuggles).

If you're doubly lucky it might be reproducible. Hard to know if the wild bugs came from the grain or your brewing environment. Just like your standard fermentation, the quality/character of your "pre" fermentation is dependent on a lot of factors (particular strains of bacteria/yeast, temperature, etc.)

Trying it again during the same time of year would be a good start. You could always monitor the wild wort, checking for fruitiness, sourness, etc. all you want...it's already "infected." I would give it a second try, and be satisfied with tasty but different results since you probably won't be able to reproduce conditions exactly.

I've been considering letting a mash (or portion of) sit out for a while, letting it get sour before sparging and boiling.

A friend of mine often let's his sparge (sometimes 20+ gallons) sit out overnight and well into the next day, getting a little funk before the boil. He never worries about it going wrong, and I've never had a bad beer from his brewery.

yeah, i think it's pretty much lacto and pedio, which should be on the grain in spades. plus the temp out of the tun is high enough that as it cools it will sit in the most beneficial range for those bugs for a bit.
i didn't detect any wild-yeasty funk, more lactic sourness. i may let it sit even longer, and keep checking on it. if i use a bucket with a tap, i won't even have to open it to get a sample.

So it only sat for 3-4 days and you boiled it AFTER it sat in storage?

If you hold the wort at a good temperature, say in the 90's, you can get a lot of sourness in just 24-48hrs. A lot of the aromatics will boil off, but the acidity will remain.

Yes, boiled the wort after the 3-4day rest.
Next time I'll probably skip the boil and pitch a clean ale yeast after it's appropriately sour.