Need help with potty-pad retraining

Hi, I'm new here, also a new dog owner as well.

2 months ago, we got a Pomeranian puppy when he was about 9 weeks old.

After 4 weeks of potty-pad training, we started to let him out of the play pen area and he was doing really well, he ran back to the potty pad whenever he needs to go.

So we started to let him out more often and longer, there was the odd accidents now and then but he used the potty-pad for the most part so we were happy with it.

2 weeks ago we started to train him to go outside, and since then he started to pee and poop all over the house when he's inside, not going back onto the potty pad as he used to.

When we started to train him outside, we initially took him to 1 corner of the backyard, but later just let him do his business anywhere in the backyard and we just cleaned it up. Does he get confused and treat inside of the house like outside and just go anywhere?

Should we now put him back in the crate and start retraining potty-pad as we did when we first got him?

I don't blame him, I think we did something wrong during this training process that confuses him, please advise.