As I remembered, PEO only stressed that your experiences should reflect what kind of design principals you used under the disipline you declared in your application form. Maybe what they mean is that the design/engineering theory you used should be within the field of your disipline.
Another question is, depite the 3 big courses you are worrying about, is that the "zhenDong" aspect not belonging to your discipline? If it is a part of your study in university, even though it is only a very small part, if only you really have experience on it and can tell the theory/principal you used confidently, you have no reason to be afraid. Just be calm and re-read the letter carefully ensure you understand it thouroughly.
Another question is, depite the 3 big courses you are worrying about, is that the "zhenDong" aspect not belonging to your discipline? If it is a part of your study in university, even though it is only a very small part, if only you really have experience on it and can tell the theory/principal you used confidently, you have no reason to be afraid. Just be calm and re-read the letter carefully ensure you understand it thouroughly.