The US owes China gazillion dollars. Not a gazillion dollars in services and stuff. That's a huge difference because at any point the US can create a gazillion dollars for virtually no effort.
The US owes China both a gazillion dollars, and additionally a gazillion dollars in stuff that dollars can buy - because they have not just US debt, but they also have currency.
Inflation is caused by too much currency chasing too few goods and services. Creating money alone won't cause inflation, that money has to actually be spent in a market where demand is already greater than or equal to supply.
One great example of inflation is the housing market. Private sector banks create money from nothing, by balance sheet expansion, every time they originate a mortgage. Because the stock of housing is less than the demand, every time the banks create more money it drives prices up. Because money in the housing market mostly stays in the housing market, that is people usually take the proceeds from a sale and put them into a new house, there isn't too much spillover to non-housing markets. The same is true for student loans.
So as you can see, two of the largest examples of inflation in the US are caused by the private sector, not Treasury spending. Please note though that the Federal Government does set banking policy as well, along with various direct and indirect guaranty programs, so in that sense ultimately they are responsible.
It will have an impact, no doubt, but probably more like a few points higher inflation than a total crash. Either way, the point is that owing money in a currency you control is vastly different than owing money in a currency you don't.
