@YorkshireFelix
I haven't had that experience, but maybe he just got confused - was he distracted when he was outside and needed longer to get down to business? Is it the only time he's done it so far? The advice I followed when mine was younger was to stay outside until she had wee'd (assuming it was a time when I thought she probably needed to go) Even down to being out with a brolly. Then a tasty treat immediately she finished.
You're going to have to prepare yourself for a difficult time at first, I'm sorry to say but that's how it is with a puppy, especially if it's all on you. Any "mistake" your puppy makes indoors will be because you missed the signs or waited too long. It's sooooo hard, yes.
I kept a toileting diary and it was sometimes 12-14 wees a day, and if she was playing it could be every 20 minutes. My main room is carpeted too, if you're lucky you have easy clean flooring..🤞
Another tip I read (probably on here) is if they don't wee when outside to not let them down, carry them, then try outside again in a little while.
I really feel for you, and hope you get some help and your pup gets the hang of it quickly.
Mine is 7 months now, she was pretty quick at learning to go outside, but even now has the occasional mishap if circumstances are different. (Workers in the home installing radiators, and then at my parents' home where they don't have a secure garden.)
Pic of my skinny minnie (and total darling) Fern.
Oh yes and I am still alive although now on antidepressants.