The reason is they are in love with him and Ayumu talking about other girl in front of them even though those two has feelings for him and told him that, who wouldn't be mad right? How about we put it like this, let's say you are either hayato or ryuji, so you confess to your long time crush. And then, things are going but your hasn't has not said yes yet. Then one day, while having lunch with your crush, he/she suddenly ask you for advice on what to do because someone confess their feelings to him/her. Even though, he hasn't even said yes to you.
Yeah it's kinda rude and insensitive
.....why was it bad when he asked them for advice after the girl confessed to him??? he was fully transparent with them and showed like zero interest in the girl plus he was just asking them cuz they've had lots of experience rejecting girls right??