What do release trains have to do with SAFe? I've worked in a few places that have the notion of a release train (roughly a mutex for "changes being shipped and a burn-in window afterwards" plus some optional batching of changes based on risk level or urgency). Only one of them even gave lip service to SAFe; others had different methodologies/levels of devops for releases/"Agile"-ness (whatever that means).

Release trains seemed like a mechanical release implementation detail in all cases; not the product or requirement of a given SDLC or process brand.