While the street thugs of the Corleone family could be expected to behave so nonchalantly, one might expect better of a well-educated person such as Tom.
Tom may have
felt differently, but it was the wrong time for him to show sentiment or feeling--it might make him appear "weak" at a time when the family's and the entire NY Mafia's structure were in flux.
IMO Tom rarely showed emotion. When Woltz flipped out on him at dinner, he replied with a nonchalant "thank you for a pleasant evening". When Soluzzo had him and said he'd killed Don Vito, Tom barely flinched.
I think he was well versed in keeping his emotions in check and to himself.
