Your guitar is now a Bb guitar = tuned down a major second. The E strings are tuned in D and also all others are a whole tone lower.
The notation is like you would read it if the instrument would be tuned in C. The instrument is transposing these chords from G down to F.
This is quite the same like the music written for all Bb-instruments like trumpet, cornet, clarinet, tenor-saxophone, baritone. All these instruments read normally sheet music notated in C and sounding in Bb. That‘s why they are called transposing instruments.
Deleted the misleading comparison of E-tuning to D-tuning.