It could be the root cause, but there could be other factors at play as well. The fact that the cluster is not correctly configured does make it difficult to identify any other potential issues though. This misconfiguration does not make clusters fail immediately and clusters can run fine for long periods of time without issues as it is only specific network/failure conditions might cause split brains. I would recommend reading the docs I linked to for more details.
This setting was often set incorrectly in earlier versions of Elasticsearch, leading to different kind of issues. This is why this area was reworked in Elasticsearch 7.0, where the setting has been removed as part of an effort to increase resilience.