What does it mean to have a sequential encoding scheme to enumerate states?

So I implemented a Mealy machine for a pattern recognizer of '1010'. I defined my states as


I then went on to do the normal combinational logic to decide where to go from each state based on the input e.g.

as well as the necessary sequential logic with the clock and reset signals and it all works fine.

I assume that this is a combinational encoding scheme to enumerate the states as they are encoded as bit patterns but as part of this project I'm asked to assume that a sequential encoding scheme to enumerate the states has been used, I don't really understand what that means. I understand that sequential logic is dependent on both present and past inputs whereas combinational logic is only dependent on present inputs but I don't see how that relates to a sequential encoding scheme to enumerate states?

Not sequential as in clocked logic but instead sequential as in a sequence, i.e. 0, 1, 2, 3 as opposed to something non-sequential, i.e. 3,1,0,2

Note the states in your state_type can have := 0/1/2/3 after each state to define what the bit values are for each state, otherwise by default they start a 0 for the left most item and increase sequentially by 1 to the right.