The only thing I can think of is that the OP studied electrical engineering at some point. But it's a 4chan story so probably fake anyway.

I think it might be the wrong way around: Engineers like to use j for imaginary numbers because i is needed for current.

Mathematicians are taught to be elastic with notation, because they tend to be taught many different interpretations of the same theory.

On the other hand engineers use more strict and consistent notation, their classes have a more practical approach.

Using the same notation makes it faster to read and apply math, a more agile approach helps with learning new theories and approaches and with being creative.