Yes and no. Each edge will be stored in groups. A group can have one or more edges. And each group will be stored in a single Alpha. But if you have replication, this data will be replicated* across the cluster accordingly to your cluster config.
In the future we gonna work in even more sharding, at the pred/edge level. But this will be something to 2021 Q4 I guess - dunno exact.
Read the paper, it might help Dgraph Whitepapers: In-Depth Insights and Analysis