That reddit comment doesn't go into much depth, do you know if that 100gbps number is actually the sat to ground budget? IIRC, the majority of the starlink satellites' bandwidth is for sat to sat transmissions (routing data from other sats to the nearest ground station).
Edit: also IIRC, SpaceX said that Starlink will offer up plans up to 1Gbps
There are currently no sat to sat transmissions, so it's all sat to ground and ground to sat.
Sat to ground and ground to sat use different frequencies so I would guess it can do roughly that speed in both directions simultaneously. There are also separate frequencies for ground stations and for user terminals, and I believe the implication was this was for user terminals. The number was just obtained by someone implying around 20gbps on the 0.9 sats and later on someone else saying something about 4-5x the speed on these sats. It's not official or likely to be particularly accurate.
Edit: also IIRC, SpaceX said that Starlink will offer up plans up to 1Gbps