The issue isn't what the injury was--e.g. that it was a cut on thumb or arm. The issue is that your friend attacked two people with a deadly weapon, and he did so deliberately and intentionally: he pulled out a knife and went back inside looking for them. That's what could easily make it attempted murder--and if he'd happened to have slashed a throat or femoral artery, he'd be looking at murder charges.It's difficult to undo a plea once given. It's almost impossible after this length of time has gone by. Being "frightened" into usually isn't enough--jail time is meant to be scary--as long as the authorities didn't lie, didn't use illegally obtained evidence, didn't deny him an attorney, etc. If your friend believes he was denied some basic rights, such as to counsel, or that he was not advised of his right to remain silent, or the evidence was tainted somehow, or the prosecutor lied to him, he should retain a criminal defense attorney to review his situation and determine if there are grounds for an appeal. If he can't afford one, he may be able to get a free attorney, such as through legal aid.