An average contender of the 70s era beating the consensus second best fighter of the early to mid 80s era is not a reasonable proposition. Lyle is getting way too much mileage for his fights with Foreman and Ali. Witherspoon is a lot more proven and has an abundance of world level wins in comparison to Lyle who is best known for losing efforts and his only elite victory being a stoppage over one-trick pony Shavers who was battering him from pillar to post before gassing out.
Who the fùck did Lyle KO to prove he could stop Witherspoon? The reverse is much more likely imo. Prime for prime witherspoon outboxes him and KOs him.
When you dig deeper his record is average. It was an era of mostly inconsistency and underachievement. He was a good fighter but i think he could have been better perhaps, like about 4 or 5 of them. He's also saved a bit imo due to not fighting Tyson, which quite a few of them did.