Is This A Change of Accounting Method?

I have a new business client that started utilizing a bookkeeper in 2020, prior to that I'm not 100% but I don't believe they were working with anyone, just their tax preparer. In 2021 the bookkeeper and client realized they were accounting for inventory incorrectly. Previously, COGS was being reported on a cash basis and no inventory was being accounted for at the end of the year. The 2021 financials given to me by the bookkeeper now reflect inventory and has a proper calculation of COGS.

Is this an accounting method change or just correcting an accounting error? Obviously there is some liability hanging over their heads with how prior years were reported, but I think the client has tried to do what is right by hiring a bookkeeper and then addressing the issue once discovered and doing an end of year inventory valuation.

Thank you!

It probably "technically" is a change from cash to accrual. If it were a small client I'd probably just start reporting ending and beginning inventory. If the IRS said anything, I'd go buy a lotto ticket the next day. If it's a bigger client then it might be better to file 3115 but it sounds like if they had this issue, chances are it's not a big client.