Freeman was the fall guy. He didn't have street smarts at the start of Half Life. It's one of his character arcs.
They knew he was from theory so he wouldn't have context to understand what he was doing. Heck, they even made it super simple for him: press button, push crystal cart into big glowy lightening thing.
Only the G-Man (and arguably Breen) understood what was about to happen. The rest of the scientists were doing the research they were told to. Freeman just happened to be on lab duty that day. One of the guards says "looks like you're in the barrel today,” which is a reference to a dirty old sailor’s joke, implying people in the lab take turns doing grunt work in the HEV suit.
If Freeman was the fall guy, it wasn't by other scientists trying to place blame on him, it was the G-Man manipulating events so that the cascade would happen on Freeman's day in the suit.
I always knew that "Gordon doesn't need to hear all this" conversation right before you go into the test chamber and fuck shit up never sat right with me