Yeah your original comment was right. When people over explain something it’s usually either that they’re not telling the truth and so they feel they have to really convince you, or they’re incredibly nervous.

If they’re nervous they might engage in that behavior even though they’re telling the truth but more commonly an excessive explanation is an attempt to create a seemingly good lie. It also makes the lie easier to pick up on because of all the details. Read my follow up comment to the guy that stuck up for the criminal and you’ll see just how funny the murderer’s alibi was.