Hello Samuel.
That is because "Relationship Finder" looks for the MRCA shared by both people.
1. Relationship between you and Stewart-1163
Your MRCA is your 17th great grandfather James IV Stewart.
2. Relationship between you and Stewart-2313
Your MRCA is your 16th great grandmother Margaret (Beauchamp) Welles (one generation closer to you than James IV Stewart).
Stewart-1163 and Steward-2313 are father-only siblings, their mothers are different. Relationship 1 is through your mother (to Stewart-1163's father).
Relationship 2 is through your father and Stewart-2313's mother. If you (temporarilly) detach your father's profile from you, relationship 2 will show exactly the same path shown in relationship 1.
The relationship between your mother and Stewart-1163 and the relationship between your mother and Stewart-2313 are exactly the same, your mother is the 15th great grandniece of both of them.
It's because it gives the closest relationship to you if there is more than one way you are related to that person. You are related to Stewart-2313 in many ways. If you look at the box below on the left where it says "Explore more" it gives a list of 320 common ancestors including his father James IV Stewart (Stewart-588) where that relationship would be 16th great grand uncle to yourself. (Although as it says in the box "Note that the relationship name will not change.")