When a church calls itself non-denominational, it usually means they decided not to put a denominational label on the sign.
Often it refers to an evangelical Protestant church that does Bible-centered preaching and contemporary worship. Still, the label itself doesn’t promise any of that and it doesn’t mean the church has no theology at all. Ask about their views on baptism, Communion, salvation, spiritual gifts or church authority and you’ll see the actual tradition pretty quickly (see this).