> DNA digital data storage is the process of encoding and decoding binary data to and from synthesized strands of DNA.

If each "bit" of DNA can be either A, C, G, or T, why call that binary?

The data is binary, the encoding doesn't have to be. Most modulation schemes in high-speed digital communication uses more than 2 states, but it doesn't make it less "digital" (in the end, everything is analog). Gigabit Ethernet's PAM-5 uses 5 different voltage levels, but one would not call it "quinary computing". Similarly, Wi-Fi's QAM-64 uses 64 possible combinations of phases and amplitudes, Base64 uses 64-symbol alphabet, but the data represented by all of them is still binary.

I think it’s kinda like modern SSDs which also have more states than just on or off per storage cell, but it’s still holding data that can be written/interpreted in binary.