Apologies I don't always have a ton of time to explain to everyone exactly what they did wrong. In this case you entered a thread about minorities and made an assertion about their lives to challenge a narrative they presented. If you had educated yourself on this issue first, you would quickly find this is a narrative often imposed on transgender individuals, one which directly effects their lives and one in which the person being discriminated against is often having to explain to the majority why their assumption is incorrect and how they are being harmed by it. If you are not the person being effected by a system you need to educate yourself before engaging with someone who is effected by the system. If your goal is to come and gather info, you should be on your best behavior- this means thanking them for engaging with you, realizing you're asking for their valuable time and energy and experience, asking questions in a very polite manner, and never attacking or making any assumptions about them.

With that being said, the general statement asserting someones sex or gender was an assumption about their life. You don't know what their legal papers say or even what country they are from. You definitely do not know their genetic information and it seems like you're not particularly knowledgeable about intersex individuals or the nuances of genetics and expression. If your intention was to reflect upon what society likely did to this person, the language needs to reflect that- for example you can state that they likely received a gender on their paperwork because a doctor decided it based primarily on the person's external appearance at time of birth. That's a very different statement from 'they are genetically this gender/sex'.