Meaning of で in 「1匹で食べています」


Consider

> 猫が3匹います
>
> 1匹で食べています

from [2m50s of this video](https://youtu.be/08zvf3XSaIk?t=170).

DeepL translates the bottom sentence as "I'm eating one of them", which I'm
pretty sure is wrong :] From context, it seems to mean "One of these cats is
eating". (But in the video the photo shows all 3 cats eating?)

Grammatically speaking, is the で after 1匹 the て-form of the copula だ, or is it
the particle で ("by means of")? In other words, does the second sentence mean
(literally speaking) "there is one (cat), and he is eating" or "Eating, by
means of one cat"?

The former makes more sense to me as an English speaker, but I was under the
impression that in Japanese the copula can't express "existence" claims (like
"there is one cat").




1匹で食べています means the cat is eating by itself. The video is a little confusing
because you can clearly see another cat in the background. Likewise 3匹で食べています
means the cats are eating in a group of three. This is the same で as in
家族で食べています (eating as a family), 一人で食べています (eating by oneself) etc, that I'm
sure you've come across before.




1匹で食べています means the cat is eating by itself. The video is a little confusing
because you can clearly see another cat in the background. Likewise 3匹で食べています
means the cats are eating in a group of three. This is the same で as in
家族で食べています (eating as a family), 一人で食べています (eating by oneself) etc, that I'm
sure you've come across before.

