The first guy taught you " Apa khabar? " literal meaning What news ? (also same as asking how are you) the reply would be "Khabar baik" meaning Good news. Since he's young guy he says Ok more informal. The Indonesian girls taught you something viral "Menyala abangku" ( literal enflame my brother) . This flame could mean to excite (Excite my brother) may even be suggestive/naughty in nature. I would not recommend using it seems inappropriate might be okay in Indonesia. In south east Asia its common to call non relatives informally as aunts and uncles brothers and sisters.
