If the hypothesis "this world is a holodeck" is normatively assigned a calibrated confidence well above 10-8, the lottery winner now has incommunicable good reason to believe they are in a holodeck. (I.e. to believe that the universe is such that most conscious observers observe ridiculously improbable positive events.)

Most conscious observers? I would think a universe/multiverse containing holodecks would still contain many people not in them. At best, you can conclude that most observers who don't see a world containing holodecks are in holodecks.

Possibly significant: the friend has some incommunicable evidence of his own – that he is conscious, in a world without holodecks, and didn't win the lottery – against (the winner)/(most observers) being in (a) holodeck(s).