I doubt they are frog eggs.
Most of the time, when the female heads to the surface to start releasing eggs, she releases them one at a time, with the male fertilizing simultaneously. Sometimes eggs are released in a group, but the release is at the surface of the water, and eggs wouldn't drop on one group of plants - they'll be all over the tank.
Sometimes I get the feeling that the whole world is against me, but deep down I know that's not true. Some of the smaller countries are neutral. Robert Orben