How do photos find their way onto an iPad's photo stream from another device?

[iMore Question]

I'm curious about how a photo that I'm told was downloaded from Internet on my husband's cell made it's way to the iPad? I'm not sure if saving a photo (j peg) from Internet to his phone (to share with his friend via mms)automatically would cross over via his linked iCloud acct. to photo stream? (previously had been enabled for sharing between devices which was disabled after my discovery). Or actually was real photo either taken or shared to his phone? What makes this more odd- within recent contacts on iPad is a co-worker of his (female) whom he's only communicated with via his cellular device. The lengths he's gone through to cover up & erase evidence since I confronted him with this only makes me more suspicious. He hacked my email & deleted file I sent to myself even after he deleted it from iPad.

 

[goku_vegeta]

I'm curious about how a photo that I'm told was downloaded from Internet on my husband's cell made it's way to the iPad? I'm not sure if saving a photo (j peg) from Internet to his phone (to share with his friend via mms)automatically would cross over via his linked iCloud acct. to photo stream? (previously had been enabled for sharing between devices which was disabled after my discovery). Or actually was real photo either taken or shared to his phone? What makes this more odd- within recent contacts on iPad is a co-worker of his (female) whom he's only communicated with via his cellular device. The lengths he's gone through to cover up & erase evidence since I confronted him with this only makes me more suspicious. He hacked my email & deleted file I sent to myself even after he deleted it from iPad.

I believe it does, now I don't use an iPhone and iPad combination, I'm only using an iPad, but this is what I gather from my use case scenario. When I've downloaded a photo (saved an image) it shows up on my iCloud photos profile through their website portal.

 

[Just_Me_D]

If Photostream and/or iCloud Photo Library is enabled on both devices using the same Apple ID and passcode, then any photo download to the Photos app will get synced.