Indeed. And while it would be possible for one male to produce two absolutely different sperm the odds against it would be astronomical.
Not only would you need to produce two entirely different sperm (I'm not sure that is possible) you would also need to impregnate two Ova to produce two viable embryos to be able to test to find out whether they were indeed different.
The odds must be totally mind-bending.
The same is true of genetics generally. It is actually statistically possible that two completely unrelated people could have identical DNA. However being statistically possible and actually happening are two very different things.