He studied 3.5 hrs studying for an exam, not counting any of the time studying the subject in the weeks and months before the exam. That sounds pretty normal. He's not saying he studied 3.5 hrs during the whole semester total and aced the course as a result.
I typically spent 0-15 minutes studying for exams because I was already prepared, always got A or A+ and usually the top score in the class at a renowned program at a top university.
I did well because most the students were not interested in design or engineering and were there because their parents wanted them to study it. These other students (by which I mean asians) would do things like get ahold of the test in advance (cheating) and get together and try to figure out the answers. But they were mostly clueless because they thought cheating would overcome their failure to meaningfully study during the semester. Cheating made their academics much worse because it was a crutch they relied upon rather than bothering to do the necessary work. But the poor results of the cheaters distorted the curve and made it relatively simple for others to get an A: it's not as if I got perfect scores. I remember one class I got something like 20% and that was the highest score in the class. Yeah, it was a difficult test, as it should have been, after all this was engineering school.
Me, I did the projects and read the assignments. Before the exam here are things you should do:
1. Do not study or think about the topic at all.
2. Drink a glass of wine the night before.
3. Go to bed early and get at least 9 hrs sleep.
This assumes you have been keeping up. If you have not been keeping up, cramming won't do squat for you except make you tired and do worse than you would have from just getting some sleep and guessing on the test.
The only studying specifically for a test I would do is to casually flip through my notes a few minutes before the test, where I'd have notes in the margins about things that were easy to get mixed up and such stuff that I had specific problems with. These things I had already spent time mastering in the months or weeks leading up to the exam, I obviously don't bother trying to learn anything for the first time at this point, that's just silly.
One last tip - don't care about grades at all. If you care about grades you'll be motivated to get high grades, which means you'll be drawn to cheat and then you'll end up not actually knowing anything in reality. By not giving a rat's ass what grades you get, you have no motivation whatsoever to get involved in cheating clubs and groups, and will study what you want when you want, and you'll do great.