How are mujoco environments used for meta-rl?

Afaik, investigating meta reinforcement learning algorithms requires a collection of two or more environments which have similar structure but are still different enough. When I read this paper it was unclear to me what the meta-training and meta-testing environments were.

For eg., a graph is given for Ant-Fwd-Bkwd showing its performance with number of gradient steps. I'm guessing these are the meta-testing performances. So, which environment was it 'meta-trained' on?

Was it meta-trained on the same Ant-Fwd-Bkwd environment?