Is using button styles for a text input bad practice?

I was recently presented with an interface that was using Bootstrap button classes for styling a text input, like so: https://jsfiddle.net/k7g2Lv43/

I personally really don't like it, and I feel like it shouldn't be done, but I couldn't explain why so I didn't say anything (I am not an UX/UI designer).

Is it bad practice, and if so why?