Bigquery gets confused by tables that have a column with the same name in CASTs, and will try to cast the entire table instead of the column.

-- causes error, as foo is a struct
select cast(`foo` as STRING) as `foo` 
from `data-playground-1234`.`myschema`.`foo`

-- works when table name is specified
select cast(`foo`.`foo` as STRING) as `foo` 
from `data-playground-1234`.`myschema`.`foo`

I think this is a simple as adding table.name here, like:

{%- set col_name = adapter.quote(table.name) + '.' + adapter.quote(col_name) if col_name in table_columns[table] else 'null' %}