iPhoto collection showing on another pc

I have a few apple products namely mine and my wife's iPhone, plus an iPad air and I have a year old iMac 21.7 pc. I use iCloud with all these devices so that info and photo's etc are passed seamlessly between these devices including emails.
An odd thing happened this morning. We received a phone call from my wives brother who was going through his pics on his pc. He found a lot of my pics on his pc. When he told me what they were, I confirmed that they are mine and are on all of our devices. We were at his house yesterday looking at his pics on the tv which he had his pc connected to. Incidently he has wifi at home.
Now my wife and I had our iPhones with us but we never used them while we were there.

Is it possible for our pics to transfer across to his system without he or I doing anything ?

Short answer, no.

He could check the last modified and last accessed dates on the photos.

Knowing the location of the pictures on his machine would help too.

Did you then or previously log into itunes or iCloud on his PC with your credentials?

I will have to speak to him regarding last modified and last accessed dates.
His pics are just in a folder on his C drive, he has a Sony lap top with windows.
I have never logged on to his pc.
Very odd.
Thanks for your reply.

If they had synced over iCloud they'd be in a very particular folder, not on the root of C.

Let us know once you have some dates please

He has been scanning his old photo,s, the type we had before digital cameras where you got them processed at a chemist shop or similar. He has been doing this most days so he has accessed and modified most days so I am not able to provide this info.
He does not trust modern pc,s so does not use iCloud, does not bank online and most of the things most of us do regularly. He does have a stand alone iPad and physically connects that to his Sony pc to transfer pics to it. But my pics are not on that.
So am at a loss to add more info to help you.
Very worrying from mine and his perspective.

So you can't see a date on 'your' photos on his machine?

The bottom line is that it is impossible to auto transfer pictures without some form of intervention. Whether that be you logging into your account on his machine, you connecting to his wifi and copying files to a shared drive etc.

That they are in a non-standard folder (one not designated as a pictures folder by the OS) further supports that no automatic process could have done that.

Was it all of your photos? The latest few? Oldest ones? A random selection? Had they been sent to him in anyway you can recall? Email? Facebook? A shared Dropbox etc?

I will speak to him again to see if I can ascertain dates on the photo,s as you describe.
He has only a few photo,s all around the 2012 period and yes they are random as there is photo,s from the other side of my family of which he has no knowledge. He did not know the people in them. So there is no reason for me ever to share them with him. I have never emailed any of the pics to him.
On sunday when we were at his house my wife left her phone behind and he called me on her phone to let me know we had left the phone behind, so we went back. Don,t know if that is relevant.
Neither of us use Facebook, twitter or any of the social media scene. Likewise dropbox or any similar things.
Don,t know what else to add really.

I can only re-iterate that automatic sharing of random content to a specific machine on a different network without any user intervention is impossible.

There will be an, as un yet discovered, fairly low tech reason for those photos being there.

However, without knowing dates (so you could see when they arrived on the machine) it's going to be near impossible to determine a cause

Sounds like someone was playing around with Photo Stream to me ...