Factory Reset macOS Sierra partition greyed out and no drop down This question is just a sanity check.
I wanted to factory reset a MacBook Pro (mid 2014) model.
I first searched the standard tutorials and such, and have the core steps down:


back up stuff
log out of everything 
command + R on restart to get to the startup menu
click disk utility
click your partition
erase and reformat (to macOS Extended or APFS)
reinstall macOS (need internet for this)


In the myriad of tutorials for this there are a few images showing each process.

In particular when selecting one's partition it often has the little arrow drop down and the partition is not grey-ed out.

When going on this mac to the same screen, there is no arrow, it just has
"Internal", then Macintosh HD (with no drop down arrow). This partition is greyed out, but I can still erase it...

Before doing so I just want to make sure that this isn't something abnormal.
Unmounted partitions appear greyed out but are still erasable, so you could try mounting the partition.

I believe the partition would not be mounted if it's hidden. I'm not sure whether it's possible to hide your base system partition though, and I don't know why you don't see the usual dropdown.