It IS possible that a person cannot detect diacetyl; some folks are blind/insensitive to it's expression.
It was almost certainly present during fermentation at some point, to some level - regardless of yeast strain (ale or lager). It's a natural production of brewer's yeast which is then up-taken at the end of fermentation at varying speeds and to varying degrees.
My experience with the 34/70 strain variants is that they are not big producers of diacetyl and ARE good, quick up-takers of D if allowed to remain some time at fermentation temperatures once reaching final gravity - given sufficient, healthy pitches of yeast. I rarely elevate my lagers to D-rest temps when using german lager strains; true czech strains, on the other hand, I give a solid D-rest.