Sahana, I think it was a combination of things ... she was flabbergasted to see him there at all ... then he came and started blasting her in front of everyone as though he was her husband ... and she had no clue why he was even angry at all, she didn't know what he had imagined about accident etc ...
besides the last few exchanges have gone like this - he kissed her, she kissed him back, he said that she and NK make a good match because both are crazy ... she doesn't know it was a response to Nani's plan ... and then when she begs him with her eyes to come with her rather than NK, he just glowers, and she goes off in a huff with NK
... so I guess it all comes together when he suddenly appears and starts shouting out of the blue and she also loses it ... see her expressions when the scene starts, she's not angry, she's confused, scared a little at his anger, wondering what's going on ... when she realises he thought she was hurt, she tries to say "hum" ... it's when he cups her face and says I thought I'd lost you, then she suddenly gets angry ... either she remembers Diwali, or she just feels, wth, he's now being all possessive and just a few hours ago he said she should be with NK ... 'make up your mind' kind of reaction!
And in the last scene, she's almost tearful when she says, what does it matter to you ... it's not anger, hardly any anger there actually ... it's as though she's at break point, and is pushing him to say it just once ... she just needs to know that yes, she does matter to him, in those words, because he has said so many times that she does NOT matter, even after and in spite of their close moments ...