Photos

Hi

Turn off iCloud photos on your mac. (Photos - preferences - icloud tab)

Once your mac is no longer connected to iCloud, then any deletions you make on your mac won't be copied to iCloud or to your phone.

Then test by deleting the images, but leave them in the recently deleted folder until you are sure they are not being deleted from the phone (leave it a few days)

If these accidentally downloaded images are the only ones that are in your Photos library, then you can also do it by simply deleting the library file (in your pictures folder). But be careful with this that you don't delete some other library that might be holding many important pictures.

MacAir is still a Mac.

Turn off iCloud photos on the device you want to delete the images from. You should have two pages of preferences, selected by the buttons top left. Click the one with the cloud symbol. It will look somthing like this depending on your MacOS version.