It seems like the game uses EGS for it's matchmaking and networking so upon downloading the game it will install something EGS-related, I am unsure if it downloads the program itself (Epic Game Store) but since the store page itself does not say anything about that I thought it be prudent to just mention that here.

I bought Perish on Steam and the game installed the "Epic Online Services" when I first launched it.

It's just like for Satisfactory, it allows you to crossplay with others platforms.
It seems an EGS account is not mandatory to play. It's optionnal. I never logged in and still able to play online.

Thank you for the information.