You selected your time zone as GMT -5, so sciforums displays all times in that time zone. It means all post times are displayed for you appropriately for the time zone you're in. That's better than displaying all times for one arbitrary time zone, don't you think?
Technically computers use UTC for time keeping. The idea being that all computers and servers can synchronise with the UTC time, it's then possible to work out GMT or any other time location from that (GMT is obviously easier since it's basically UTC, although GMT can have daylight savings applied) GMT was likely set initially because of the London based site owners.