YMMV but to me his tone made him sound like "wut?". He wasn't expecting a zinger from Kirk. The 5th draft of the script has Kirk saying "I beg your pardon?", and the revised 5th Tan pages (revision color) has Kirk's reply as "Earth. Germany. 1938." And while there's a clear scene direction for Chang to play the "To be or not to be" bit "with a malicious twinkle" there's no such clue-stick for how to play the "I beg your pardon" line, except that it indicates Kerla "hastily" interjects thereafter, which suggests Kerla was trying to smooth over the awkward moment Chang just got caught in.
TUC Trivia: It's still Saavik in revised 5th draft pages as late as June 14, 1991, well into principle photography, and I've seen a call sheet for June 20 what identifies Kim Catrall playing Valeris, so my guess is they changed the name so late they didn't bother to change the script pages to avoid confusion with the various departments. They just changed it the few times it was said in dialog.