Well I had applied a while back and had been trying to delay my interview coz I didn't expect such a quick response. As opposed to come who have had to wait 2-3 months before receiving the first email.
I guess being typed and currently flying the 737NG helped my case. I was originally invited in July so it was a case of a delayed slot for me. At least 2-3 other guys of the 7 in my group had similar circumstances. 1 guy only came for the sim because when he was originally there for the interview, the sim had a problem. So maybe they have delayed more interviews for now, but luckily I had gone through the hoops before that.