Which one of these two ISO 639-2 code refers to Traditional Chinese, chi or zho?
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.