Is it possible to be "good" in one area of "applied mathematics" yet "bad" in another?

Let me explain, I did my AP courses in HS and got into a good EE program, I fell in love with the "Mathematical Introduction to Electromagnetics" course which basically taught us the essentials of vector calculus (it was taken for granted that you knew the AP stuff so you could start with multivar functions ,partial derivatives etc).

I was great at it, really good at it, and so I even helped other students do their HW etc and got a perfect grade on it and the subsequent engineering electromagnetic courses.

I seem to have a knack for spatial reasoning so no wonder it was really "engaging" for me.

I'm trying to teach myself statistics now because I will likely go for a masters and PhD now and oh boy, it's just a mess. The earlier things went well where I reduced everything to a visual manipulation of sets, subsets their orders and cardinalities but things just keep throwing curve balls at you from no-where.

Was I just lucky to do well in multivar calc and pdes or what?