Pasteurized lambic beer has continued fermenting

Hi all,

Well it is hard to me to understand what´s happened with my first pasteurized bottled lambic beer.
I have several bottles of lambic beer that I have brewed using my captured yeast(I have posted many posts a while back), I let them sit at room temp for weeks because they are pasteurized and I have not much available room in the fridges. This beer was clear ,tasted a bit malty sweet because I let it ferment only 90 days and it has a very low bitterness addition with a very subtle sourness almost unnoticeable, so it is clear that I bottled it too soon.
The point is : last night I opened a bottle and poured a very hazy fizzy beer that smelled very good but tasted so much more sour than it tasted at bottling time and has much more carbonation(it was force-carbonated in the keg to 1.8 vol before bottling ).
I haven´t got too much experience in regards sour beer taste, it tastes very sour(not undrinkable) and its Ph is 3.4. Maybe I´ve made a mistake at the moment I took FG before bottling because it was 1005 and now it is 1005 as well , but it is undoubtable that fermentation has continued inside the bottles, but how can this be possible?. I personally have pasteurized this beer before bottling , I have warmed it up to 186 F during several minutes, it took at least 15 mins to cool this beer down before transferring it to a keg, there should be no microbe alive after this procedure.Keg and lines were sanitized as usually, I have never had issues at this stage.
Pedio doesn´t produce Co2 while fermenting, so I wouldn´t think this microbe is the culprit.Could lactobacillus have survived pasteurization?
I am disorientated.

 

I think the process failed because I couldn´t cool beer immediatly , it took me sometime ,so the pasteurization hot-sudden cold process didn´t take place properly.

 

I opened 2 bottles, the same result. The only way I think it could have been a chance of contamination is when i left the hot pot without the lid during 15-20 min to let it cool. It was in my backyard, but that was beer instead wort, there was alcohol , I doubt it though.