Is it $25 k or $30 k?
What this may prove is that he's a better negotiator than you are.
How long has he been licensed as compared to you? Does he have additional licenses?
It sure sounds that you were lied to, doesn't it? Perhaps the other new employee's training at the other bank had used software or some application that is specific to the job?
If you say something too specific about salary differential of newbies to your hirer, you risk your future or the other person's future there. If you are vague and don't name your source but call the hirer on their lie to you.. you could run risk, as well.
The trouble is that you would have to point the finger at the other new guy as your source unless you can figure out how to express it. HR people categorically advise strongly against discussing their salaries.
You have a serious issue. Perhaps someone else can help you better than I can. In this woeful hiring environment, you may have to think long and hard about this...but you really have an issue and that is with HR.
I know as recent as 5 years ago in this situation the HR of a major corporation I worked for was willing to disclose the salary ranges in terms of percentiles when reviewing salaries of people with similar experience. They showed the salary brackets of all current employees in my same situation based on their experience and time in the position. HR at ML could have the same arrangement..or not.