Could be :)
I mainly assumed based on color of the "Liquid" (oils and similar were instantly excluded, based on probability of getting these liquids served in such arrangement). While scotch, whisky, bourbon & maybe even rum aren't strong, pure enough (based on density, drink must have at least 86% of alcohol for ice to sink to bottom). Tea or coffee are mainly water. So the only argument left for me was, that those "Ice rocks" are basically made of glass. Then they would keep cold, wouldn't melt, would sink to bottom & have different IOR. Problem could easily be solved, if title weren't so descriptive. ;)
Yet still, there's so much detail missing to stop any speculative guessing... ;)