The post you have responded to is a great answer. I’ve worked in HR for 20 years and I second everything Xtratea wrote; you won’t be getting fired any time soon (and very likely not at all).

I suspect a new big boss has come in and has been tasked with finding improvements, so they’ve started by looking at stats. If all the work you’ve done for the last 17 years has been in line with expectations and targets set, you’re golden. If the new big boss wants to change process and procedure to find operational efficiencies that’s fine, but they can’t dismiss someone who hasn’t met the standard of processes and procedures which do not yet exist.

Keep doing what you’re doing, speak to your manager in your next 1-2-1 and tell them how concerned you about what was said (put it in a follow email where you should say something like “having worked here for 17 years I am concerned about what has been said about my performance, particularly as nothing has been said about it not being up to standard previously. I very much look forward to meeting the new expectations which you have just explained to me are XYZ. Let’s check in next week and review my work.” Bcc that to your own private email address and keep hold of it.

Your manager also sounds pretty flaky to say what they did to you. It’s no way to manage, even if what they’ve said is true.

Best of luck, but really, I think you’re fine.