It would help if you specified which course you are referring to.

I disagree with your idea. I think if the instructions tell you to pick all the answers that apply, it should only give full credit if you actually pick all the answers that apply.  Why would it be better to count it as correct if the user misses some of the correct answers?  How would that show that the user understands the lesson?

You've got a point, but it doesn't really count it as correct. And it also lets them see they aren't getting it fully, and gets them to think about it more to get the right answer.

I'm fine with the app showing which selected ones are part of the answers that apply.  That's different from counting an incomplete answer as being correct.