"He is not a girl."
Translation:El nu e o fată.
People get bored of saying "este" over and over in actual speech. We just shortened it to "e" for the third person. This also happens with "trebuie" which often becomes "tre" in speech.
Example: "Tre sa merg la scoala" = I have to go to school (spoken language)
It's just a difference between spoken and written language.