It would appear that he is talking about "multicoin" wallets:
Exodus - Multi coin, closed source
Coinomi - Multi coin, semi open source (apparently very outdated repo)
Jaxx - Multi coin, technically not "open source" as such, but apparently you can view the code.

So, I'd suggest checking out the code that is available for Jaxx and/or Coinomi if you want some idea of how "multi coin" wallets are coded