PIP Advice please

Hello - I put in a PIP application for my son (age 17) at the beginning of April (last month). 
I thought we wouldn't hear anything until summer, given backlog, but out-of-the-blue a lady from Capita rang (from a mobile number) 3 weeks ago.  We hadn't had a letter or any correspondence to confirm she'd be calling and  I was out at the time (so couldn't support him on call) but when I came back my son said she basically said 'as you've answered we can do the online assessment now'.
He wasn't really prepared but told the truth and we just hoped it was enough. 
Anyway, a week later she rang again - this time my mobile - as she couldn't get through on the landline, to check some queries on the mobility issue and said she'd submit the form to DWP that day.
I rang DWP last week - about a week after the last call - and they were very surprised.  They said calling without any notice sounded very unprofessional, that normally Capita are working on much older cases and they'd be surprised that they'd picked up my son's so quickly - as it was only submitted the previous month.  They also said they hadn't received any report back from Capita.
I don't think it was a hoax as the lady certainly knew her stuff and was referencing what we'd put in the form and had mine and my son's numbers. 
I'm just confused as to what is going on and whether I should sit tight - and hope that they did do my son's PIP assessment early - or if I should query with Capita on their published number? I don't want to rock the boat if it does look like we might get an early decision but the whole thing just feels a bit odd given the general backlogs, the way she rang from a mobile number, and no report reaching DWP.
Would appreciate any thoughts/experience on same. 
Many thanks in advance