Hi,
Recently I was speaking to a friend ane mentioned that I liked a certain band.
Him: this song always seems to calm me down totally
Me: Coldplay are good
Him: no, coldplay is good, but the members in it are good

Him: A band is a single item, so hence you can only use the single conjugation of a verb, not the plural
Now I don't consider myself a pedant but I do find it rather embarassing when my English is corrected. Can anyone elaborate as to whether he is correct and a general background on the convention itself?
Thanks