Fantastic news csr1, I’m here to answer your questions!
quick disclaimer,: I havent seen the video you mention, but I’m assuming its some sort of kiruv promoting stuff
” But what does this have to do with Tisha B’Av. ”
1) Chazal tell us that the beis hamikdash was destroyed because of sinas chinam. What better way to rectify that than by promoting love among klal yisorel, and what better way to show love for klal yisorel than to bring them closer to Hashem
2) how sad that on Tissha baav so many don’t know what we once had, sadder still they don’t know what we have today and could have tomorrow if enough of us want it. The onl yway they will know about the churban, is for us to be mekarev them
3) As a result of this galus we have lost many to assimilation etc. There lack of observence is only as a result of the churban
hope those help!
Anything else I can help you with?