They did it only after ES decided to abandon the Apache license. I doubt that Amazon would have done it if they were not forced.
Redshift is also Postgres based and Amazon never released something. So based on that metric Alibaba is more open.
There would be no open source Elastic had Amazon not taken it on. It was a smart move and benefits their balance sheet to do so. The point though is that move was greater than replicating existing open source work.