You're quite right, GP is being mistakenly over-broad. Mimivirus (APMV) is an encapsidated virus, and the capsid is what forms that shape. Capsids[1] generally contain the DNA or RNA of the virus' genome and often appear quite geometric. Capsids have a T-number, which determines how many faces of triangles or hexagons+pentagons exist. It's a deeply mathematical field of study since these are, essentially, tiny repetitive building blocks.
Some (tobacco mosaic virus being the most famous) are helical, while others (bacteriophages) look completely different[2]. Viruses appearing spherical are generally enveloped, meaning they contain part of the cellular plasma membrane surrounding their capsid (HIV). Ebola is part of the filovirus family[3], which are characterized by, among other things, their long, filamentous shape (hence the name).
1: https://en.wikipedia.org/wiki/Capsid