I was delayed 18 hours by Qatar in October, instead of being in Singapore, I spent a day in Doha. They had to pay me compensation of €1,200 Euros (after initially refusing to pay anything), so this is not an isolated incident.
But were you delayed by 18 hours leaving EDI though? A small delay can of course lead to a misconnection, but that's hardly unique to QR.
According to the Scotsman today QR is actually the most punctual airline at EDI, based on CAA figures, so yes, last week appears to be an isolated incident. As unfortunate as it was for those involved.