If you REALLY want to know:
Try yourself. See how far you get in a month... or, if you got the nerve, in a year. You will be amazed how long EVERYTHING takes as soon as "it works, somehow" is not good enough anymore. Sure, you can kitbash a game in some days, and it will work, somehow.
But hand THAT game out to 5 people and see it fail the test. It will break down because of bugs, and quality issues. THIS is what will take you most of your time, testing, ensuring some quality standarts, testing again, and then, testing once again.
The fact you think that a) developing a small 2D game should be quick and easy, and b) a major in CS makes you a lone wolf indie dev just by sheer awesomeness of the degree makes it look like you never REALLY tried game development... something that takes years to really get into and understand even if you only try to master a single discipline.
A lone wolf needs to be at least competent in many. A CS Degree will not help in creating art. You can outsource it, you still need to have an idea as at the end of the day, there is no one to integrate the art other than you. Similar about sound, game design, marketing, and customer support.
You can bet at least months, maybe years of the devs time were spent for marketing and business.
Now, I have to say I don't know about the game and the dev. But there is a chance the guy didn't work on the game fulltime. If you only work 8 hours per week on a game, that game takes anywhere from 5-10 times longer to develop (seeing how usual game dev weeks can be up to 80 hours of work in cases of bad crunch)... so if he was working on the game in his free time, it might only have taken him 6 months working fulltime.
The second thing is that even with a CS major, the guy might have spent 2-3 years learning the ropes, and not really being all that efficient working on his project. I can tell you that a CS major does NOT make you a senior programmer at all... you are a junior at best (the very best coming out of a CS major might be usable as juniors from day one, the others only as trainees). And that doesn't include all the stuff you need to learn for effectively developing games (not talking about art and sound and all the other stuff yet, just programming).
Studying and getting a degree teaches you some basics, and gives you a degree to find a job with. It does NOT train you as a specialist. That can only be done on the job (and you don't really need a degree to become a specialist, only to have a better chance in the job market).
The last thing to remember is that you don't come up with a project that sells a million copys just like that... not even the game dev stars can do that. If you wake up one day with a brilliant idea, are able to pull it off without any delay, and it happens to work out fine and is fun at the end, that is like winning the lottery. Most of the time this is a process, where 10 projects are consecutively started, 7 of them abandoned in early stages as they just suck, 3 being developed further, and only 1 of it really the big hit everyone is looking for.
Game development is often very experimental, hands on. Creating prototypes, testing them, and throwing them away quickly if they don't work is the usual process of successfull devs. That means a lot of time lost to experiments.