No, YOU are confused. The reason the $US became the reserve currency was because it was convertible to gold, so the paper was AS GOOD AS GOLD! Countries were not giving their production to the USA in exchange for a promissory note (as they do now), back then it was an entitlement to gold. So it was the equivalent to barter, exchanging manufactured goods for money with INTRINSIC value. The USA defaulted on its obligations when Nixon removed the convertibility in 1971.
If a country can simply print money that has no intrinsic value, why would anyone trade with them? It doesn't make sense at all. Think of an island nation that wants to import widgets manufactured in China. According to you, all the island nation has to do is simply rip some bark off a tree, write some numbers on it, declare it legal tender then send it to China and expect manufactured widgets in return. Would you send your manufactured goods to the island nation in return for bits of bark with numbers on it? No sane person would!
Do you honestly believe that because the USA can PRINT the reserve currency that it has the right to consume what the world produces?
If you were selling your car for £5000- and someone turned up with a piece of paper and wrote "I owe you £5000" on it, would you give them your car?
If someone turned up with 5 ounces of gold (that you assayed to be sure) would you give them your car?
Do you see the difference between money with intrinsic value and a promissory note?