SEC rules and the Sarbanes-Oxley Act impose heightened obligation on the CFO of a public company, including the requirement to certify the company's periodic financial statements. Given the importance of this role, Nasdaq generally requires listed companies to employ a full-time CFO.
First of all, I couldn't find anything in the actual Nasdaq Capital Market Listing Requirements regarding a CFO being mandatory. Considering the size of the company and the simplicity of the financial record keeping, the controller would suffice.
In fact, if you give the whole boring thing a read, there's very little preventing SGLB from uplisting.
I did notice this tidbit in the Corporate Governance Requirements
These requirements include rules relating to a Company's board of directors, including audit committees and Independent Director oversight of executive compensation and the director nomination process; code of conduct; shareholder meetings, including proxy solicitation and quorum; review of related party transactions; and shareholder approval, including voting rights.
Maybe that recent communication we received is just another box that's been ticked.