Is there a way to
gunzip a file that isn't ending with a
.zip even though I know for a fact the file is indeed a zip?
There are two issues here. gunzip can be used to decompress any single file compressed with gzip regardless of the file's extension.
gunzip < file > output file
A zip file (one containing multiple compressed files) is incompatible with gunzip. For this kind of file, you need to use unzip. unzip can decompress any zip file (not gzip) regardless of extension.
Also, the extension doesn't matter in linux, and is simply for human-reference.