I know they are two different countries, I was talking about in terms of interior design.
此句有两处错误。
about 和 in terms of 内容重复，删掉一个。
第二分句没有连词却用了逗号。需要加并列连词 and 或 but。
I know they are two different countries, and（but）I was talking about interior design.
我知道它们是两个不同的国家，而我刚才说的是室内设计。