From the way this post is written, I think you don’t realize how vague your communication style is. Too many possible interpretations of what you said makes it hard to even follow the story you laid out.
Who emailed who about what?
How did someone resend an email that someone else sent?
Re-sending would mean the same coworker sent the email twice.
On rereading, I think you meant that one coworker sent an email to the client, then another coworker that you are having trouble with also sent the same email to the same client.
So, to answer your question, I think they arrive at a different conclusion because they see things differently. Anything that can be interpreted differently will be interpreted differently. The other co workers think they’re giving this person set values when in fact they’re handing them a set of variables and expecting only one result.