That's because it is Shogo's voice that you hear. The credits list two people as Won, I din't remember the first name listed, but the second name is Kazuki Yao, who played Shogo in Megazone 23 part 2.
According to a translation of the Megazone 23 timeline, the Dezalg aren't aliens, but instead are genetically engineered humans that colonized Mars.
Here's a link to said timeline:
http://mickey.cis.yale.edu/eve/mzonebg.html