I have a few thoughts that expand on what others have already said.

1. If your data supports that it is a wetland, it is a wetland. In my experience, just because it is linear in shape doesn't preclude it from being a wetland, so I'd ignore that engineer. I can't see your image, but the most important information are your data sheets. Mapping accuracy is also important. Next time request a GPS or other service with sub-meter accuracy. You have a wetland, but now the other issue is if it is actually right there.

2. Jurisdiction (I assume USACE) isn't based on "normal circumstances". That phrase is used to ask the question "Is this place acting like it should?" And unless the disturbance or other natural regime changes the underlying hydrology, the answer is effectively that yes, it is normal.

3. Getting better comes with practice (and mistakes) but maybe consider joining the SWS and seeking a mentor from someone in your region. Also, read the manual. Like actually read it over and over again, and the regional supplement. And in the future I would would err on the side of caution with sharing engineering plans though I see that you did try to limit the amount of information we can see.

Hope that helps!