If it's early release it's a warehouse leak most likely that then gets dumped from a modded console (xci format). Some users convert xci to nsp for reasons unknown to me. Might be that switch cartridges have extra padding at the beginning/end that can be stripped to reduce file size.
Otherwise it's just a standard dump from a modded console in either eShop (nsp) or physical (xci) format
In case this was asked in earnest, yes- it happens all the time. Nintendo releases have been notoriously leaky for about 3 years now