That's because, looking at the "Fibre in the UK, see when fibre arrives" box, you are looking at a very old
marketing message. 19th April 2011 was when Plusnet started selling fibre connections, so every exchange that was already in service got labelled with this date.
And because it is a static marketing message, I don't think it has been updated *since* 19th April either.
If you use the "Check availability" buttons, you get a better answer. Or you need to use a live dynamic checker that tells you about the current status of your own individual line, such as:
http://www.dslchecker.bt.com/adsl/adslchecker.welcome
However, both of those will dpend on the same BT database that you've now disappeared from. You might need to wait until it comes back.