To your point, perhaps it has involved luck, but I don't think it's very odd for people to double their money before losing it all when following martingale.
No, it's not unusual. It just has to happen less than half the time on average, due to the house edge. Otherwise this simple strategy would be profitable:
* start with X; martingale until doubling; quit
If you successfully double Y% of the time, your expected profit would be:
(Y*X - (100-Y)*X) / 100
= X(2Y - 100) / 100
which is positive exactly when 2Y > 100, ie. when Y > 50%