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".