I don't have the broader context (like the exact situation for LGBTQIA+ people in Tanzania), but...

> Yah I'm sure the African pycon was planning to ask every attendee if they are LGBT...

You're passing judgement on people you don't know, while you remain in a privileged and ignorant position. Many trans/NB/intersex people could be easily identified as such, based on their appearance/voice/etc. Even if the concern was sexuality alone (or other characteristics you could mask/hide), nobody wants to live out their life in a closet - that's also the entire point of a conference: to go there and talk to other people, to feel safe while doing so, to be able to remain yourself.

The problem space is way more nuanced than "just don't have gay sex in public lol".