>Is this common? I’ve had access to company credit cards before on a one-off basis (never in my name). Do people legitimately make this mistake? “oops, I put it on the company cards”?

It's worse than that, because he specifically entered the company card to pay for robux. It's not like he added the company card for an earlier (company) purchase and then it accidentally got used.

>Dave said he entered the company card himself to buy Robux for his son, and it then sat saved on the Google account that also carries his work email, calendar, and files. Dave did not say why he used the company card for that purchase.

Moreover I can't think of any reason why he would be using the company card in the first place. In any company with proper controls you'd have to justify every expense and/or reimburse. It's just simpler to use a personal card, unless he was trying to embezzle some money.

Whenever I've had a company card, it's basically been for the company's benefit except to the degree that large purchases hit my personal credit limits. There may be exceptions like paying for events but I've never been in that situation. But, generally speaking, company purchases on a company credit card are going on an expense report like anything else.