Not all engineering graduates become engineers, or stay "pure" (hands-on, technical) engineers. Practicing engineers (i.e., in specific enumerated fields where incompetence directly risks the safety of the general public) can often be distinguished by state licensing (such as "Engineer in Training" (EIT) or "Professional Engineer" (PE)), though that may not be required for engineers employed by larger companies (the "Industrial Exemption"). Not sure how far along Padilla went along the EIT/PE path, but Aerospace, like Hughes where Padilla first worked, is one of those fields where most engineers work for larger companies and are not licensed. Even those who initially work as engineers may go on to related fields. A typical technical engineering career may last an average of seven years, with engineers transitioning to other jobs, like management, "Systems Engineering" (essentially Program Management, working with part selection, vendor relationships, staffing, and budgets, with the math closer to accounting than scientific), even medicine or patent law.
Padilla's engineering career faced challenges with the Cold War draw-down of defense budgets, and he found passions elsewhere fighting for the rights and dignity of fellow Hispanics. Others trained as engineers, like Lee Iacocca at Ford and later Chrysler, found the work experience too dry and overspecialized (in his case, designing modulators in automatic transmissions) and moved into sales and management. There's no implied professional failure in doing engineering for a while, then moving on if something else stokes your passions stronger.
Similarly, not all politicians are, or should be, lawyers. Our Founding Fathers anticipated that our representatives would come from all walks of life. This may be important to understand other than the strictly legal implications of legislation and public policy. Some of our better and most effective representatives (IMHO) also come from the fields of military service, medicine, and business, for example.