Is text length really a sign of disinterest?

I feel pathetic enough asking this, or judging a guys level of interest on a text message (something that was designed to be brief and to the point, anyway) but I'm always reading that if a guy responds with a short message, he's not interested in you, give up, etc. This guy loves talking one on one with me for hours, but he's not much of a texter. He always replies to me though, even to texts I accidentally send (meant for someone else) it's just not anything to continue the conversation (e.g he'll write "haha...yes") It makes sense that a guy interested in a girl would take the opportunity to turn texting into a conversation, asking her questions, etc, especially if he's too shy to initiate, but that s**t does cost money, too. I feel like the fact he even replies at all is good enough, but maybe marathon text messaging sessions is the true sign of interest. So is short texts really a sign to give up on a guy?