This is talking about sexuality, not gender identity. Who you want to have sex with is not determined by your sex or gender. It is correlated, but not determined (as in more cis men are bi and straight than gay, thus a random man is more likely to be bi or straight than gay).

In this case, she's talking about her preferences which can be any identity, sex etc.

For example, a trans person may prefer to date other trans people because they will have more common experiences and there will be less explaining if how things work on their body etc. Others might have preferences based on primary or secondary sex characteristics. Others may only date people who like a specific type of cheese.

An individual person can do whatever they want.

It sounds surprising to me that trans people broadly prefer trans people is all.