I will attempt a crude picture.
Filter Mode:
Pump -> Backwash Valve -> Gauge -> Sand -> Backwash Valve -> Return plumbing
Backwash Mode:
Pump -> Backwash Valve -> Sand (reversed) -> Gauge -> Backwash Valve -> Backwash plumbing
So in backwash mode, the pressure gauge is only measuring the pressure loss of the backwash valve and backwash plumbing. In filter mode, the gauge is measuring the pressure loss of the sand, backwash valve and return side plumbing. Different plumbing results in different pressure.
Also, the pressure loss is dependent on the filter size and I believe in your case, you have a very large filter while the OP has a smaller filter. The pressure differential will also depend on the plumbing down stream from the filter so pipe/fitting size and number eyeballs and eyeball size will have an affect. Most AG pools have only one eyeball and usually 3/4" so the head loss is quite high just for that. Your plumbing is probably much different than the OPs plumbing so there will be a big difference in pressure experienced in backwash vs filter modes.