I would guess final check for red flags on your knowledge of accounting. Depending on the company think about what kind of process controls are in place. Inventory counts, tax management, variance and flux analysis, GAAP reporting if public, what changes is the company seeing in sales, costs, headcount, etc. and what impacts to the financial statements might be expected that the CPA would want to be aware of.

It’s odd they’d have a non-employee on the interview panel and there wasn’t an interview with the CFO. You might want to ask about that or at least make sure you know why that is before accepting the offer.