Ok, thanks. Don't suppose you have a link to anything where that is officially stated please? I like to know these things for sure if I'm going to pass further comment on them.
Bottle tops: https://www.brightonandhovealbion.com/news/2019/january/supporters-reminded-on-prohibited-items/
I can't find any mention of terrorism in relation to flasks, it was mentioned on the flask megathread but I can't find a direct quote from the club:https://nortr3nixy.nimpr.uk/showthread.php?366302-Flasks-banned-from-the-Amex
One of the problems some people had with the bans was how poorly they were justified. Terrorism was never a reason given by the club, but by fans who supported the club's decision. The explanation for the bottle tops came in January 2019 after a few high profile bottle throwing incidents at other games, the ban was put into place in August 2018 before said high profile incidents (and to fill the gap in explanation for the bans those fans citing terrorism for flasks, were citing the threat of slipping on a capped bottle during an emergency exit as the reason for the bottle top ban).