I don't think you read the post carefully enough: they were not running a distributed monolith, and every service was using different dependencies (versions of them).
This meant that it was costly to maintain and caused a lot of confusion, especially with internal dependencies (shared libraries): this is the trade-off they did not like and wanted to move away from.
They moved away from this in multiple steps, first one of those being making it a "distributed monolith" (as per your implied definition) by putting services in a monorepo and then making them use the same dependency versions (before finally making them a single service too).
This meant that it was costly to maintain and caused a lot of confusion, especially with internal dependencies (shared libraries): this is the trade-off they did not like and wanted to move away from.
They moved away from this in multiple steps, first one of those being making it a "distributed monolith" (as per your implied definition) by putting services in a monorepo and then making them use the same dependency versions (before finally making them a single service too).