I think the short answer according to both old-school and... what's it called?... modern monetary theory (something like that) is that whether it causes a lot of inflation or little or none depends on excess capacity in the economy.
If there's enough excess capacity in the economy to absorb that new money, there's no inflation or very little. So if I have a plant running at 80% and I get a 10% boost due to the new money, that doesn't appreciably drive inflation. But when the government money drives businesses to make choices - I can serve this customer or that customer - because they're at 95% when they get the 10% boost, then it's strongly inflationary.
The hard part with a giant infusion of money is knowing what the actual capacity of the economy is.