NET 90 and asking for special quotes from big companies is definitely something that happens all the time. I'd say that is being stingy with payments. (It should be normal of course, but... that's what contractors often deal with)
These are not the same thing as simply refusing to pay your bills.
"Net 90" is not "Net Whenever/Never".
Also the terms should be an agreement, but in practice it's: the large company has more power and will tell you their finance dept will not pay out before X - doesn't matter what you put on the invoice.
If the story here was just "Twitter is late paying its Google Cloud bill, and Google is giving Twitter additional time to pay in full", then that wouldn't even be much of a story.
I've even been on the other side of that, expensing it because that was easier in our system than getting a PO.