No. I’ve never heard this before. It’s true that scientists don’t always write the clearest code, but Fortran, and even the style of Fortran typically written by engineers and physicists, is comparatively straightforward to read. It is named for FORmula TRANsator, after all. You will recognize the equations in the code. Fortran is inherently easier to read than C; it’s really not harder to read than Python. You can make it hard to read by doing complicated array indexing tricks, of course, and there are sometimes good reasons to resort to that.
And no one except other domain experts will ever have any interest in looking at your source. Why would they? No one except someone designing a website will ever want to try to figure out your CSS either.