No, I don't think you need an attorney at this point.
What ultimately will happen here is that the question will get referred to someone in OWCP's national office. That person should set the CE and his supervisor straight as long as they are clear about the fact that the pension is from a state or local govenrment agency.
You did not earn your entitement to his pension from your Federal employment. You earned it from your non-Federal employment. It should not make any difference to OWCP because it is not one of hte reasons foir alterning your LWEC. (Besides, I bet this pension probably won't pay as well as your earnings from your current employment. OWCP certainly is not going to adjust the LWEC upward just because you voluntarily chose to retire.
If you were a FERS employee during your Federal career (or CSRS offset), then you did pay into Social Security as a Federal employee. Some, but not all of your future SSA retirement benefit will be based upon your Federal employment. There will be some affect on your LWEC once you start receiving SSA retirement benefits. It won't be the entire SSA benefit because it looks like a significant portion of your SSA retirement benefit will be from non-Federal employment (including military service, if applicable). But there likely will be an offset applied to the LWEC for the portion of your SSA retirement benefit that is attributed to your Federal employment. This is not a one size fits all offset. If you only had a few years of Federal employment, the offset could be very modest. If your Federal career was fairly lengthy, then it could be more substantial.
Cross that bridge when you get to it. It is not likely to become issue until you start collecting SSA retirement benefits, which can't happen for anyone before age 62.