your irl friend is wrong k
genderfluid is changing between genders (could b literally any gender k)
transgender is being trans, which is not being cis, which means that you aren't the gender you were assigned at birth.
example of genders: agender, female, demigirl, male, demiboy etc. some ppl might be more than one gender, and some people's gender changes w time n stuff.
but like, if male is a yellow crayon and female is an orange crayon and agender is a red crayon to make things simple. someone can hold both a yellow and a red crayon!! that means they're bigender, but bigender isn't actually a gender (/crayon), it is just a combination of crayons/genders. lol