Maybe by "experimental technique" they meant "a technique that is used in experiments",
Indeed. It is an "experimental technique" rather than a "theoretical technique" or a "computational technique", say. It's frustrating to read an abstract of a physics paper which sounds like the authors have performed a nifty measurement, only to find that in fact they are proposing an idea, or have performed a simulation, or theoretically analysed the problem. (Don't get me wrong, they're all equally important things, but not the same as performing an experiment). Thus, it's nice to emphasise one's "experimental technique".
They are called computers simply because computation is the only significant job that has so far been given to them.