The website TerpTheatre is dedicated to: Sign Language Interpreting for the Theatre.

So, if you invite someone called "TerpTheatre" to your event, it's probably to talk about sign language for theatre performances. However, the event wasn't providing sign language interpretation. So - he did a presentation in sign language so that people could experience not knowing what is being said, and let them know that's what he was doing.

I was a student chair on a community college curriculum committee (deciding degree requirements, mostly) and one of the professors was a CODA. I know ASL, as did he, and there was a big argument as to whether or not ASL should meet the language requirement. Most professors said no, as it's American and they wanted us to learn a second language spoken abroad. Ultimately, we only communicated in ASL until they budged on it. The only exception for ASL counting now is for students in certain transfer agreement programs to schools that won't accept ASL. I've since left the school but I hope it hasn't reverted back.

I wish Sign Language was used in schools right from an early age so children become naturally bilingual in it.

It has so many useful implications even outside the accessibility piece that I wish kids took it too. The only thing I'd be worried about is that if it was offered at every school, it would become removed from Deaf culture. I've found people are more than willing to share Deaf culture, but we can't remove the language from the context of the community who created it. It is really beautiful, and the first time I saw a Deaf kid at work (science museum) and he realized he could communicate with me in his language, his eyes just lit up and it was totally worth it.

I'm sorry but I didn't really understand?

There was an event about (probably) disabilities, and the organizers invited a man who works with deaf people to give a presentation on deaf issues. But they deliberately didn't arrange for interpretation (translation from spoken English to American Sign Language, so the deaf people in attendance can follow along) and probably other disabilities, too. The man instead gives a presentation in American Sign Language, to show that the organizers don't actually give a shit about deaf people and wanted to debate deaf issues without involving any deaf people.

Hm I think he did the best thing then, and thank you for explaining!