Imagine if you were the CTO of a company, massively underestimated your AWS bill, and presented your board with something enormous. Maybe something like that happened?
Or, if I wanted to speculate to the extremely negative; what if the training and operating costs ballooned to such a degree, that the deal with Microsoft was an attempt to plug the cash hole without having to go to the board requesting an enormous loan? Because the fact that Copilot (edit: previously known as Bing Chat and Bing Image Creator) is free and ChatGPT (edit: and DALL-E 3) are not should be a red flag...
Unless there was evidence you had not underestimated but were, e.g., getting a kickback on the cloud costs that you deliverately lowballed in your estimates, they might fire you, but they almost certainly wouldn't put out a press release about it being for your failure to be candid.
That language indicates that the board has a strong belief that there was a major lie to the board or an ongoing pattern of systematic misrepresentation, or a combination.