It releases lots of energy proportional to the mass, yes, but one proton + one anti-proton annihilating at a time, it's a very small explosion. And they only had 38 anti-protons.
I believe that one of the the articles quotes one of the Physicists saying that it "wouldn't even warm up a cup of coffee"
Edit here you go:
Prof Rob Thompson, head of physics and astronomy at the University of Calgary, one of the 42 Alpha investigators, said: 'This is a major discovery. ... We've been able to trap about 38 atoms, which is an incredibly small amount, nothing like what we would need to power Star Trek's Starship Enterprise or even to heat a cup of coffee.'
It's not very much in everyday units.
"Atoms are neutral - they have no net charge - but they have a little magnetic character," explained Jeff Hangst of Aarhus University in Denmark, one of the collaborators on the Alpha antihydrogen trapping project.
"You can think of them as small compass needles, so they can be deflected using magnetic fields. We build a strong 'magnetic bottle' around where we produce the antihydrogen and, if they're not moving too quickly, they are trapped," he told BBC News.
Such sculpted magnetic fields that make up the magnetic bottle are not particularly strong, so the trick was to make antihydrogen atoms that didn't have much energy - that is, they were slow-moving.
So, basically, magic. I'm just curious what the specific limitation is (but realize it may not be trivial to explain without understanding the entire containment process better).
Neutral atoms still have a magnetic moment. These do interact with magnetic fields. I'm way over my head here, so won't attempt to explain more.