Of course it can be jammed , technology is there just needs the authorisation.
Not really if its flying autonomously, as there is no signal to jam (assuming its being done maliciously by somebody with half an ounce of intelligence). The Flight Controller (aka Autopilot) is pre-programmed with waypoints to fly to. And that's also what makes it so hard to locate those responsible (assuming they don't want the drone back, else you just need to track where it lands and monitor that).
A £25 Flight Controller, and £7 GPS/compass loaded up with free open source software is all that is needed to fly autonomously. And all multirotor drones have a flight controller of some description (too unstable to fly without), and the vast, vast majority have GPS capability.
Obviously, if its being manually flown, there will be a link, usually 2.4Ghz for short range (couple of km, so less likely in this case) or 900Mhz for long range (10km). The trouble is, most links frequency hop to prevent interference - hence you can have a load of people flying together on the same frequency, with none of that tosh of sticking flags on you transmitter that you did in the old days - meaning you'd have to jam the whole frequency range and at high power. Jamming 900Mhz would piss off the mobile networks and their customers, and potentially impact TV. Jamming 2.4Ghz would piss off just about everyone.