Someone made a chemistry joke that went over your head. Dextrose is sugar. Common in corn syrup, to be exact.
Yes, but the volume is higher than granular sugar. It's a "bulking agent" to give the sweetener a pleasing volume.
Dextrose is sugar just like cellulose is sugar.
How is dextrose in a sugar packet filler? That makes no sense to me. Maybe it's just a confusion of terms.
I believe parent meant a packet of Splenda, not actual sugar. However, it would not be surprising if packets of "sugar" actually contained dextrose as a bulking agent.
Maybe they meant cellulose?
Cellulose is used as an anti-caking/anti-clumping additive. It doesn't add bulk like the puffed up dextrose or maltodextrin does.