I'm guessing that actual incidences of engine failure are quite a bit higher than that... anybody care to guess how frequent?
If you are speaking of engine stoppages where it never restarted:
Without doubt that is true for
twins, where an enroute engine failure should be a non-event and would not be reported unless somebody wants to drag someone's nose through the dirt to draw attention to bad maintenance**. EFATOs often kill everyone aboard (they require good pilot currency) which helps to swell up the fatal accident stats for twins (another factor is the typically more demanding mission profiles flown in twins).
It may also be true for
singles. I am certainly aware of cases (years ago) where somebody landed a school plane in a field, an instructor went to retrieve it, and flew it back, and no fault was found or reported. Maybe carb heat, who knows? But this would be very rare, because fields landings are not easy to cover up.
It has been suggested that engine failures are more common in twins than in singles; reasons offered have been a) more vibration, due to the engine being less rigidly mounted on the wing spars than on a single's firewall; b) longer control cable runs; c) longer fuel pipe runs; d) a pilot of a twin will be less aware of something "funny" with the engine because it is further away, so a fault can develop unnoticed; e) some twin owners, particularly some commercial operators, definitely have a less critical attitude to maintenance, running on condition, etc because they have a spare engine. The last one is controversial but enough twin owners have made this very clear that I don't doubt it for a moment
Diamond went to avgas for their US sales of the DA40 but they continued to sell the Thielert DA42 out there. Go figure, as they say...
** Early on in my TB20 ownership, I had loads of problems with autopilot failures. (Actually they continued but got a lot less bad). One failure which happened with me not present, with the pilot who was an instructor (the fake-ATP one I referred to in previous postings) reporting that the aircraft was nearly inverted within seconds, was something I wanted to MOR. I was discouraged from doing this by various people, him included, on the grounds that a MOR will stick like the proverbial to a blanket. I am now less than 100% sure this incident actually happened (for reasons too long winded to go into here) but I did contact the CAA and they weren't too bothered about it.