Chrome OS now uses your primary account to set up and manage Play Store access and Android apps for you. That means the account that you use for your Play Store access is same as the Gmail ID that you use to log into your Chromebook. You could log into different apps using the secondary account, but Play Store remains with the primary account.
This might be changing.
A recent code commit talks about “Separation of Chrome OS and Play Store Accounts”. This could mean that you could have a separate Google account for your Play Store access. This opens up a lot of possibilities.
However, I am not quite sure why the Mozilla Firefox package is mentioned within the code though:
My basic Googling tells me that com.android.vending is the package name for Play Store, so that sounds alright.
I would need help from Android developers here to understand this piece of code. If you know what this means, please drop-in a comment.