Likewise, did MGS2 actually happen?
By all of it. MGS2 colonel was not the real Campbell but an AI-generated personality. He still exists.
Beside above, is the Colonel real in MGS2? Emma Emmerich eventually uploaded a virus onto Arsenal Gear's systems, which caused the Colonel to start acting very strangely. During the infiltration of Arsenal Gear, Otacon concluded that the Colonel was in fact an advanced AI and not a real person.
Also to know is, is MGS2 a VR simulation?
The major plot points of MGS2 did happen, and their repercussions carry over into MGS4. However, all the absurdities prove that what we play in MGS2 is a VR simulation. In the same vein, we're just playing a VR simulation of the canon Big Shell incident, but with minor changes.
Was big shell a simulation?
The Big Shell was real. It was a simulation, not virtual reality. Meaning, the entire events of the Big Shell were set up to test the Patriots' AI (or rather, the S3 program). The events actually happened.