Presumably the file .bash_history starts with non-text data, hence grep is treating the file as binary. This is confirmed by the file .bash_history output:
.bash_history: data
You can read a few bytes from start to have a conforming view:
head -c1K .bash_history
Here I am reading first 1 KiB.
You can pipe the STDOUT to hexdump/od or similar.
As a side note, grep takes filename(s) as argument, so cat is useless here; try this:
grep git .bash_history
