I suspect the real problem is simply definition... just like people call most tissue you can blow your nose in "Kleenex" even when made by a different company, so goes things like ERD's and the like. There are about 20 different types of ERD's and, yes, some of them look like process flow charts and others look like table relationship diagrams. Both can qualify as an ERD because a person, place, or thing can be an "entity" and so can tables.

I suspect the type of ERD your instructor is looking for doesn't have much to do with "data modeling"... rather it's likely more like a table relationship diagram being sought after.

Here's an example of that...

http://rapidapplicationdevelopment.blogspot.com/2007/06/entity-relationship-diagram-example.html