That is a normal looking cage for Shimano's 12 speed derailleurs. While the M5100 is marketed as 11 speeds, it's designed exclusively for the Shimano HG 11 to 51 toothed cassette. This is a common spread of gearing for 12 speed systems (M6100, M7100, M8100, M9100). These utilize the Hyperglide + system, which is a set of design and engineering tweaks to the derailleur parallelogram and cage, cassette shift ramps and tooth profile, chain design, and chainring tooth design. The largest 3 cassette cogs of the M5100 cassette is actually a Hyperglide + design as is the shape and slight offset of the M5100 rear derailleur cage. So, despite being an 11 speed derailleur, it utilizes the 12 speed tech so that it can smoothly climb up and down that wide range, 11 speed, 11-51 tooth cassette.
Here are somewhat poor photos of a 12 speed, XT derailleur (RD-M8100). The first two are the same photo, I've just added a reference line to maybe help see the offset. The third pic is the same derailleur but I've pinched the cable stop and pinch bolt together to move the parallelogram out of the way.
