I see your general point. However, nobody is getting issued a $20K loan in advance of installation and having to pay on it prior to installation. That's not how any bank works.
Also, lets remember that the backlog is spread across three offices now: Sunworks, Sunworks Nevada, & MD Energy.
Further, SLTD did that PR stating that they had a record sales month in March, which of course is the last month of the reporting quarter. So, much of the residential backlog (if any) was likely jobs that were on schedule, but had just been booked.
However, the March record was only $2.1 Million residential sales. If that was the high month for residential sales, then it means much of the backlog is commercial jobs, which always take much longer to plan & execute.