Character mistake: In the opening narration, John Connor says that he was attacked by the T-1000 when he was 13 years old. This is wrong. In Terminator 2, we see that John Connor is only 10 years old, as shown on the police computer when the T-1000 accesses it. (00:02:20)
Character mistake: When the Terminator scans the doorman at the bar, a display comes up categorizing each piece of the doorman's clothing. The word "briefs" is misspelled "breifs". (00:13:40)
Answer: The difference there would be suicide vs sacrifice. In T2, basically what he meant is he could not commit suicide as it was against his programming. They had beat the T-1000 and had won, but it was too dangerous for Terminator to stick around and knew he had to be destroyed. But he could not purposely do it to himself as it was an act of suicide. However in T3, it was a sacrificial move. The goal of his actions was not to destroy himself, it was to take out the TX and prevent her from reaching John. He had to do this by any means necessary and made a sacrifice play by shoving his core into her mouth and blowing them both up. It wasn't suicide this way, it wasn't self termination. He was taking her out but caused himself to be collateral damage.
Quantom X ★
Also, after watching that scene again, I'm adding this little tidbit. The Terminator didn't actually die from the thing he did to the TX in that move. If you notice towards the end after the nuclear bombs go off, the fall out ash is falling down around its head and its eyes are still on, slowly fading away. It was badly damaged by its move, but the bombs in the end finished him off.
Quantom X ★