I'm just playing the odds here.
It seems more likely that a young man who deeply embarrassed himself and became a national pariah (unfairly) for a few days would then create a scenario that made his actions seem more justified. That's just human nature.
On the other hand, if you believe Rudolph did this, then none of his teammates heard him say it (and they were all in earshot) or they all agreed to stay mum and protect their backup QB which they have limited affinity for. Or even possibly the NFL itself is covering it up because they would likely have access to audio of it since mics are all over on a prime-time televised game. Why would the NFL risk covering up a racial slur for a backup scrub QB? They will throw any player under the bus to protect their business.
I'm a Cleveland fan, so I want Myles to be right. But it just doesn't seem likely.