They sold first, and the sale contract carried a long settlement.
That one term did the heavy lifting. The price was agreed with no pressure on them at all, and instead of a month to find their next home they had a genuine window to look properly, miss out on one or two and still be completely comfortable.
Shane had their finance organised while that window was running, so when the right property came up they could move on it immediately. They bought for $1.420 million, and the purchase contract was written so its settlement date lined up with the settlement on the sale.
That is a simultaneous settlement. Both matters settle on the same day and the proceeds from the sale flow straight through to the purchase. There is never a day where they own two homes, and never a day where they own none.
Aligning the dates also meant no bridging finance was needed anywhere in the structure. Bridging is the usual answer to this problem and it does the job well when you need it, but it brings a second set of loan costs and interest on a peak debt figure. Here the timing did the work instead.