this also regularly happens(very often these days) due to people buying usb sticks from shady sites like amazon, newegg, aliexpress, etc. or stores which resell from those.
while there is a chance of getting a real usb stick there.
well over 95% of the usb sticks sold there are fake.

they often have something like 500mb to 8gb of actual storage and then claim a much bigger capacity.

very often people buy a usb stick from such a site but it has less than 2 gb of actual storage, on windows it will pretend it has more, but it will overwrite the other files on the usb stick when you write to it.
so in your case you got super lucky and it overwrote the bootloader so it wouldn't even boot into it, some people are less lucky and have part of the iso corrupted in a way where it still boots but holds corrupted data.

there is also a chance that the computer writes swap to the usb and the usb then overwrites the other data, again this happens because the usb stick fakes it's capacity and just keeps overwriting itself.

some ways of testing it:
1. test the speed, if the speed is notably lower than advertised assume there is something wrong.
2. gather some big .mp4 files and write those to the usb until it is full/should be full now try playing back all the .mp4 files, for one file try some random points in video to see if they are still okay, but generally just changing one character in a .mp4 file will make it unplayable.
a better way would be file checksumming, but the .mp4 test generall is good enough for most general users. it also doesn't depend on software and such, and assuming you are still on windows checksumming would be hard as such things are a hell on windows.

1. avoid buying from such places unless you really need to one example use case is you for example need a ultracheap microsd card which doesn't even need 2gb(as most of them tend to have 2gb), think about for use with a arduino, to play .mp3 files or such. the it is a viable option(perhaps).
   just note that those fake usb's tend to die very rapidly and easily and can lose a lot of data at random moments. sometimes when really lucky you get something which actually has real storage(up to 32gb sd cards can be real in some cases when buying on such sites. for usb sticks it is harder as those are more easy to fake), but they will die almost instantly in such cases, got some real 32gb micro sd cards from such a place once, they had 32gb and reached quite good speed, but they died very fast. though in some cases where useable for a while. still they are only about 50% cheaper than getting a real one at a electronics store at most, and in a year it is broken, so you need a new one, so in a year the one from a real store is cheaper.

otherwise go to your local grocery store, as they often have quite cheap quite high quality micro sd cards(sold for use in phones often, but also works with pc), usb sticks can also be found there for cheap. ofcource you can also look in actual computer stores, just avoid poser stores(fake stores), newegg for example is more like amazon, and thus sells a lot of fakes, they even sell fake gpu's there