Tier 2 extension - supporting docs back in one week

Hi All,

I submitted my Tier 2 general visa extension (along with 2 dependents) application online on 17th April and posted documents & gave biometrics on 18th April.
I got all the supporting documents back today including both the passport size photographs.
There is a note included which read: "Thank you for supporting evidence. This is to confirm your documents have been received and your application is with UKVI for consideration."
Is it normal to receive supporting documents back so quickly on a standard application? Also, why do they ask for photos and send them back?
Has anyone had such a experience?
Thanks for your replies.
VK

In the meanwhile, I gathered information that if the applicant's sponsor is 'A-rated Premium' then they send passports back very quickly. Can anyone corroborate this please?
What I still dont understand is why they sent the photos back? Any suggestions on if I should be writing to UKVI and ask to send them back?
PS: They have also sent me an ID card of some other applicant by mistake! I told them about this over the phone and they said, they will get in touch with me.