I had this store card that would send me a $0.00 sheet with nothing else on it. I'm thinking problem is the computer prints it out and packs the letter. The only human interaction is someone having to pick up the box of envelopes and take it to the mail. So no actual human is really aware or doing it on purpose. I'm thinking a lot of companies waste a lot of resources doing this. If you think about it if some store has 100k customers, and each month prints just 1k at a rate of .01 per page that's 10 dollars which doesn't sound like a lot but if you factor in the number of months, years, etc you got a lot of wasted money.
My thought is it's some sort of bug in the payroll software. Maybe they "closed" your account and the glitch is that it automatically prints a check and deposit it into the bank if it has an account. Maybe the developer forgot to do a check to see if balance > 0.00 or maybe it's a requirement that regardless of balance it prints and deposits the amount.
I think you should just ignore it unless you want them to be aware of the glitch. I would only bring it up if it is frequently happening as it would be annoying.
Edit: My answer is based on no knowledge of any sort of laws. I'm just stating from a common sense perspective but it may be some sort of law requirement in your state or country. Regardless it's a one time thing usually and I would just ignore it and not do anything for now. Only bring it up if you're seeing it on a interval.