Adding water after beer is kegged

[RickyBeers]

My Elvis juice clone turned out around 7.5% and easy to drink, so let’s just say it was dangerous.
I wanted to drop the abv, so I added 3 water bottles (20 oz PET bottles) of spring water using a carb cap through the gas post. I made sure that I squeezed the bottle and capped it where the water was all the way to the brim, hoping I reduced as much oxygen as possible.
Otherwise, it was simple, just released head pressure in keg and stuck 30 psi on the PET bottle. Seemed all good.
Well, beer sucks now. Low IQ move by me. But what I’m wondering is, did I introduce oxygen somehow this way? I swear my beer tastes oxidized now but I’m not sure if I’m just picking apart everything I don’t like about it since I added water.

 

[JAReeves]

I am sure someone with more experience than I will pipe in, but the dissolved O2 level in the water probably is the oxidation culprit.

 

[day_trippr]

I don't have any experience with post-carbonation adds but I would agree the water was the likely instigator...