This is not uncommon. They are still juveniles and trying to figure out this whole parenthood thing. One of them could have gotten cold feet - er, fins - and decided to eat the eggs while the other one slept.
But since they did lay eggs, it means they will continue to lay them. As they get older and wiser, they will get proficient at it - at least, that's the plan.
Some angelfish books and experts will tell you that angelfish don't know how to care for the eggs, the hatchlings, or the babies. But I have found them to be excellent parents if they're only given the chance for their own trials and errors.
