A wiggy (your non-contact voltage tester) can sense a voltage where there is no wattage, i.e. no amperage. If it's not connected to a power source, your length of cable is merely acting as an antenna, but there is no power, and no hazard, present.

If it is still live, it is a big deal. Hot tub lines have higher amperage and are double voltage to standard outlet power. Turn off the breaker or pull the fuse to the wire, hopefully it is labeled. Also, if your non contact voltage tester is one of the cheaper ones, they can read false positives after they wear out, it is a common thing that happens. The line might actually be turned off already. I had a cheap one and had to get rid of it after like a year, it read voltage when the line was dead. I got one of the better klein voltage testers and you have to directly touch the hot wire or stick it in the hot plug on an outlet to check for live, very low chance for false positives.