Were they actually being dishonest about it, or were they not disclosing it? There are a lot of things people don't disclose before meeting up. Outside of a romantic relationship context, cis people tend to be more accepting of trans people in general if the cis people don't know right away that the person is trans and find out later.

But for sexual/romantic relationships it's different because most people want to know the genitals of their potential partners up front. This makes it difficult for trans people, who are stuck deciding at what point they should disclose the state of their genitals, in a way that is considered honest, keeps them safe, and maintains some privacy.