Partying wasn't the first thing that ever really came to Izu's mind when it came to completing training exorcises, his sensei would normally have them do several dozen push ups and sprints as reward for succeeding at training. Konoha ninja were happy go luck and didn't have the serious and super trough training that Mist shinobi had to go through. But since his master wasn't here, Izu saw no problem in a little partying as long as there was meat and fish to be had. It also would help him recover chakra and he did feel his stomach growl from hunger

"Sure I'll join, I hope there's meat I'm pretty hungry" he replied to Rin. When he heard Seth talk about making something for the party, Izu's mind thought about really hard liqueur and people becoming incredibly drunk. This made him chuckle to himself at the thought. Izu didn't know how to get to the grill so he had to follow the Uchiha, which was annoying because it felt like taking the lead ahead of the ninja, but he had no choice but to follow.