I'd really like to think that it's you, rather than your attorney, who's mixed up on this. That would be understandable. Your attorney being mixed up like that would not be. Assuming that the proposed pretrial diversion doesn't bar expunction altogether, you'll be able to get your records expunged as long as you successfully complete the program, at whatever date the contract says you can get an expunction.
If you take the deferred adjudication option, on the other hand, you'll probably be able to get your records sealed by an order of nondisclosure at some point fairly soon after you complete probation (it's not guaranteed, but most judges will do it). However, unlike with an expunction, records that have been nondisclosed are still available to law enforcement and certain state agencies (so they can prevent you from entering certain career fields and can be considered against you if you ever get arrested again). If you get an expunction, the records will actually be destroyed, and legally, it just never happened, so usually, that would be the better option for most people. Either way, though, you will have to file a separate case at a later point for that to happen--neither an expunction nor a nondisclosure ever happens automatically.
A pretrial diversion is better. Once completed, you can file for an expunction that will eliminate the records to everyone. A deferred adjudication, after successful completion, is entitled to a petition for nondisclosure, which seals the records to the general public but not to law enforcement and governmental licensing agencies. These agencies are the Texas Bar, FDIC, and many others. So if you try to get a job as a professional or at a bank, they will still be able to see it. Additionally, a nondisclosure is something that is discretionary. You are not entitled to it, so a judge can deny you getting one if its not in the "best interests of society". You are entitled to an expunction if you qualify.