Changing File / Saving / Pull?

Hello,

i have a simple general question about changing files -

When i open a file in IJ and do some changes, but do not save the file. After that i closed the IJ-program (i am not prompted if i want to save files...) and reopened the file - the changes were still in the file.

How could that happen? Shouldn´t there be a prompting if i want to save the changes when i leave the program?

And after that i tried zu pull the old file from github - but this was also not working - told me that the file is actual - how could this happen?

Finally i went to github - copied the whole old file and changed it in the file in IJ... - but this can´t be the only way...

Can somebody enligthen me pls...