It was never open source before apple. Rather the binary was freely available to be used. When apple bought them they took it away but continued to support customers with contracts. In that way it was inaccessible until it was open sourced.
Yes, I got bitten by this and will never forget- FDB abruptly shut off public access in mid-2015. Fortunately for me, it only cost half a day to migrate my system to Postgres.
I'm sorry I mis-remembered the exact details of another team that I didn't work on and tech stack from 8 years ago. I'll go give myself 100 hail Marys.
The point wasn't to bash Apple - the point was that the team lost a lot of money and time and shipped and inferior product because Apple chose to purchase and close down part of the stack.
And here's a news story - https://www.forbes.com/sites/benkepes/2015/03/25/a-cautionar...