Yep, that’s pretty much it. You didn’t make a mistake by pushing though, pushing with a shield is supposed to still block just fine!
It’s just that, as explained in the report, there are some block actions for some of shields that, despite being able to block both melee and ranged, they can’t block unblockables (either melee or ranged). But some of them can, like aiming with the Shotpistol shield, or pushing with it.