>>127404667
you COULD write it out as a key change but it would be clunky and make the sheet music more busy than it needs to be

compared to Major(ionian), Lydian and Mixolydian only have one sharp or flat difference. it just means for that chord, they're leaning on that one note change. seeing as the rest of the chord and melody still retain the sound on the original key, it doesn't sound dissonant, just a little mysterious. then they go straight back into the same key so it's just a quick nod or wink, musically speaking