It's easy to believe that a student pilot has never pumped their own fuel, for all the reasons others have mentioned. In addition, where is it on the ACS? It's not, and therefore it's likely not in most training syllabi and therefore unless a CFI specifically takes the time to train on it (which they should), it's perfectly believable that they've never done it.
And if you've never been shown, it certainly could seem daunting. I mean just look at the typical self-serve fuel pump - there are switches and buttons and knobs all over the place. It's nothing like the gas pump for your car which is about as simplified as you can get. Let alone the card interfaces are typically awful and you have the additional steps of grounding the plane and (usually) turning the pump on. And then retracting the hose and grounding wire, etc. Of course, none of it is hard but it definitely isn't intuitive when the simplicity of auto gas pumps is our experience.
Any time something like this comes up - "what do you mean you don't know how to do (insert seemingly simple task here)?" I am reminded of this story I've told here before about my daughter and soap:
It's like when my daughter was about 3, we were in a hotel. She uses the bathroom and comes out looking very troubled.
"What's wrong honey?"
"There's no soap!"
I go into the bathroom, sure enough there's the bar of soap I had unwrapped earlier, next to the sink.
"It's right there, silly"
"Where?"
"That bar of soap right there."
"Bar soap? I don't know how to use bar soap!"
Which seems really ridiculous and still makes us laugh, but I paused a moment before responding, and realized that, actually, she probably didn't know how. All of the soap at our house is in the pump containers. So she may never HAVE used bar soap, and I never thought of it to teach her. It wasn't on my "child training syllabus". It was then that I realized MOST things are taught, not intuitive or obvious, and to blame the teacher (i.e. me) for lack of knowledge, not the student.