"Clicked Link" level of confidence?

We use G Suite for our enterprise email. 

I recently conducted a phishing campaign and some of the users that are reported as "Clicked Link" are adamant that they did not click any links in the email.

I cannot find any documentation as to what Sophos' level of confidence is when they report that a user "Clicked Link"

We want to initiate remedial training for users, but we also want to make sure they in fact need it.

Thank you in advance.