Everything changes after the over-head bridge

I'm reminded of this incident when i'm chatting with the guys.(aka my grouchy neighbour and kenneth)
there is this one saturday when i'm in hall then since got no meals provided then so muz go out to find dinner. So the guys(aka the above mentioned and me) decided to go clementi to grab a bite. so we went to the bus-stop to wait for a bus, then while we were waiting, we saw 2 gals from our block who also going out for dinner. lets call them B and C, then it so happened that they were also going to clementi for dinner. so we all boarded the same bus, then when alighted at clementi, i went to ask B if they wanted to eat dinner together with us, B agreed, then we all had to climb an over-head bridge to get to clementi.
But everything changes after the over-head bridge,
suddenly C tells us that they have to go "buy" some stuff and won't be joining us for dinner.
wat the hell?
y the attitude is so different? y so fast flip and change decision?
Sigh...
i think i know the reason, but it's not me,(i hope..)