Yes and no. They should have tried to be more understanding, but so should Buffy. She was gone for months, and didn't even bother to give them a call! They had no idea if they were ever gonna see her again, or if she was even alive. I'd be pretty mad myself! And also, we don't know everything that happened that summer between the scoobies. Seemed to me like Wilow had been really upset the whole summer cos she worried so much about Buffy. We all know how protective Xander can be over Willow, and I think that was part of the reason he was so mad.
They all seemed to be avoiding the topic at first, trying not to talk about it. I think they were worried they'd yell at her. But when Willow saw Buffy packing again, she just couldn't hold it in anymore. And when it had first started, Xander couldn't hold back anymore either.
And I also think it was good for them to get it out. If they hadn't, it might have been lying there underneath the surface, and in the long run could have ruined their friendship. Noone should ever bottle up their feelings!