That's the same, old vendor lock-in approach. It has happened with the servers, databases, network equipment etc. now it happens with cloud -- nothing unexpected, prepare to see more of these when cloud market stabilizes and clear leaders emerge. That's why I always prefer open solutions, that can be moved/migrated/replaced easily and advise others to do the same.
They certainly should have communicated that better and their tools / charts should have a way of showing the billable data, but it's a bit of a stretch to call it vendor lock-in. It's not like everyone on Firebase is complaining and the author admits they made major mistakes.