If the builder is unsure of the structure, to determine whether the gyprock wall is part of the structure, walls may hold up the roof as well as define rooms. Engineers are the go
You may need a lintel, where the wall was, or columns to support the load, especially if there is an upstairs above this wall.
Engineers can determine the load bearing structure needed to hold the load above, to be tied in to existing structure.
Floor plans make it easier (less $), the engineer can determine from inspecting the structure, but it costs more.
Whatever the engineer costs before, is less than remediation after
The builder didnt just gut it and "Oops".
I think thats a good sign
builder skill-integrity-commitment is not always present.
Holmes on homes shows a lot of the gut it and run types, season 9 here