That’s correct. The Ruby client still uses the older Batch Direct protocol. The difference between these two batch protocols is explained in the Aerospike documentation; a discussion of the impact of migrations on batch requests using the Batch Direct protocol can be found in this forum thread.
The only possible work-around for the Ruby client is to use single-key requests instead of batch requests. Adding a feature to the client to wait for the migration to finish (as suggested by that TODO) is not a viable solution, as migrations can potentially take a long time. The better solution would be to implement the Batch Index protocol.