Which one of these two ISO 639-2 code refers to Traditional Chinese, chi or zho? On a database file, the designer uses chi and zho to tell simplified Chinese and traditional Chinese. It's hard to tell whether chi means the simplified one or traditional.

Seemingly, chi is derived from the first three characters of "Chinese", zho from the first three of "Zhōngwén".

The wiki page of Chinese language, as well as the following two links from ISO 639 documentation, chi and zho, all tell us that chi is ISO 639-2/B, where the B stands for bibliographic, zho being ISO 639-2/T, T for terminological. The explanation of the B and T codes does not shed any light on traditional-or-simplified information the either.

But there is nowhere that I can refer to showing which one representing the traditional Chinese.
chi and zho stands for the Chinese language, but not one of its writing forms.

Specific codes for traditional Chinese and simplified Chinese widely in use being zh-Hant and zh-Hans respectively, specified by IETF and also RFC 5646.

The use of improvised codes "tc" and "sc", which abbreviate "Traditional Chinese" and "Simplified Chinese", are often observed too in Chinese websites.

So, just as @TactMayers said in the comment, I also think that the designer chose them deliberately, or simply due to misunderstanding.

By the way, here may not be a right place for this question; Stack Overflow is more suitable.