The notes on the 5 lines are the melody notes, not the strumming pattern so use the strumming pattern provided. Hopes that clears it.

I grew up like you with the notes called Do, Re, Mi but the first band I joined the singer used the same system but the rest of the musicians used the C,D,E system so I learned that quickly and now I don't even have to think about it and can switch between the systems in an eye blinc.