It only confuses people who actually know the technically correct time zone designations and choose to be pedantic about it.
No, that isn't right. Those people probably aren't actually confused at all. The people who are confused include anyone who for any reason has to look it up.
I'm a godless foreigner, trying to co-ordinate a game with players in the American Eastern and Central time zones. The only time zone offsets that I actually know are Australian Eastern Time, Central Time, and Western Time. So when a player says that he is free at, say, 8 PM EST I have to look it up to make sure whether American EST is UTC-04, UTC-05, or UTC-06. I just don't have the details of foreign time zones at my fingertips.
And when I do look it up, I get mislead. All standard references tell me one thing, when the players have meant another. And now that I know I can never feel sure whether any particular poster is using the official or the colloquial terminology.