Yes, twist that. Counterclockwise.
It's a long T bolt that secures the spare tire and keeps it from shifting around.
It may be very tight, and perhaps a bit rusty (given the corrosion on the rim). You may need "channellock" style pliers to get it started.
You would be prudent to put some anti-seize or grease on the threads before putting it back.
You might also find that the tire is "stuck" to the floorpan of the trunk; you may need a stick or prybar to break it free.
Good news is you'll find all sorts of great stuff underneath the spare - old coins, dirt, rust, gunk, dead bugs, a bolt or two, that can of Underwood's Deviled Ham you swore you bought at the grocer seven years ago . . .
On Edit: Sorry, I meant " . . .tyre stuck to the floorpan of the boot". I got lazy and forgot to translate. Apologies.