Mista and Trish didn't know that Bruno was dead for good.
Polnareff made a blunder and revealed it to them - he notices his mistake on the top panel, when he catches sight of Giorno's expression.
Trish and Mista make small talk so as to distract themselves and avoid crying over Bruno's death.
Yeah, that's no "It's raining", granted.
The epilogue was very sad, however.