Mods. The pistol, AK, glove with watch, vest over shirt and hoodies, some of the vest themselves, are all impossible to either obtain or combine Online.
Saying that, they mostly look like texture variations/ model swaps which you can go online with (depending on how OpenIV is injected), but it'd mean that other players won't see your changes unless they have whatever RPFs you've modified yourself in their game.
In FiveM, there's stuff you can do specific to the servers - so if all the above was part of a pack, then anyone who connected to that FiveM server would likely already have the available assets and thus, everyone can see what's being used (and what's been changed).
Anyway this thread can mostly be buried now - I don't think there's going to be the same sort of 'levels of mischief' affecting other people's games like we had in the past anymore.