It could be that they have a wall for posting things. Instead of a bulletin board this person has a whole wall. Or a team of people are painting a room and this person is painting this wall. Or it could be like when my children had a "time out" to cool off or to think about what they did bad, they each had their own wall to go to.
As far as I understand it, you're correct. I know that Germans have the advantage of "gendered it's". My teacher gave me this example:
"Der Tisch ist kaput und die Lampe ist hell." (The table is broken and the lamp is light.) "Sie kostet 10 Euro und er kostet 20 Euro." (It cost 10 Euro and it cost 20 Euro).
The English phrase is ambiguous, but the German one is not. (First lamp, then table.)
Das ist meine Wand = That is my wall
Es ist meine Wand = It is my wall
"It" is used to point out an object or an animal and is interchangeable with this, that, etc. That is used as more specific saying the object is far, opposite of "this"
That over there is my house
this is my pen (holding it or at reachable by hand with no significant effort)