As BillJ said, Spock wasn't always the stoic, coldly logical character early in TOS, this Spock HASN'T led the same life as Spock Prime, and we never saw Spock under the emotional pressures he is under in ST09 in TOS. . .so really, you can't say how TOS Spock would react. . .
Considering how utterly gutted he looked when he thought he'd killed Kirk I think snapping when his whole planet had blown up was expected.