You fell for a very old urban legend. Please google it before spreading "friend who worked corporate finance at one of the big casinos" stories. Your friend was just having fun at your expense, as was the family member.
This is actually true that they can and do adjust the odds on these machines for high rollers and the like. It's all done by computer now, no lever. However, there are strict procedures involved. If there is a player on the machine, you can't change the odds or payouts without first kicking the player off the machine, and you have to make the payouts very clear (usually with a placard on the machine), and you have to change that too.
Looks like there’s actually some truth to it. Wouldn’t be surprised by some exaggeration but please google it before leaving a comment dismissing it.