Disclaimer: I'm not an attorney nor can any advice on here be taken as anything but an uneducated opinion.
Expungement: Physically destroyed. No record remains after an expungement.
Sealed: Record is sealed but retained. Can be accessed only with a court order.
Unless a document is provided by a court or agency after an expungement or sealing that states you may now state said action never happened, then I would advise disclosing it. The FAA is an administrative agency so falls outside of the protections afforded under the criminal justice system. Unless you received a written notice stating that you "may properly reply to a question into the matter that no such record exists", it would be wise to disclose it?
You can conduct a pretty exhaustive background check on yourself, fairly easily. Fingerprints through an FBI channeller will get you the criminal history records. The NDR will provide records of serious driving infractions. A query of each states DMV's will provide a detailed driving record going back 10 years. I'd imagine someone who went to court would remember which state/jurisdiction the court was in, and is able to query those records as well. I have no criminal or driving history, but still conducted a thorough check on myself, overall cost about $100. The agencies aren't perfect and mistakes can be made. I'd prefer any issues or errors not show up on Indoc Day 2.