There's clearly something very wrong here - have you reported this to iStock?
It's great that you're finding these, but with more than one image containing elements from multiple other portfolios, this isn't some inadvertent slip up and this person's portfolio needs to be shut down.
don't know if this is the same person or not. but about 6 years ago, a student pointed out to me of a certain photo-collage "artist" who is well-known in her circle and have lots of her work on the web.
in that moment of discussion, the student showed me pages of google of this person's work.
the student also mentioned to me that this collage-artist actually states that she uses other photographer/artist/etc work without permission and that she is actually making money out of her collage.
i wish i could remember that student, so i could contact her to find out this collage artist's name and show it here. but maybe someone here knows about this collage artist too.