Apple iMessage recieves from others apple id
Hey guys, I've recently updated to ios 8.1.2 and I iMessaged my friend and then it sent as a text which isn't a problem but then I got a reply back and it had his apple id and was using iMessage. Then I went into the original conversation it still sent as a text and at the bar where your write it says "Text Message" but then when I go into the conversation with my friends apple id it says "iMessage". I'm not really quite sure why it is doing this. I'm using AT&T's 4G in my house along with my homes wifi. I thought turning off my phone and then turning it back on would fix the problem but it didn't. Then I thought deleting my contact then re-adding it would fix the problem but it didn't. I have an iPhone 5S What is going on?
Thanks for the help!!
iPhone 5s, iOS 8.1.2