I would appreciate some clarification on the "store 4 bits of data with one transistor" part.

This doesn't sound remotely possible, but I am here to be convinced.

They declined to say: https://www.eetimes.com/taalas-specializes-to-extremes-for-e...

Except they say it's fully digital, so not an analog multiplier

Fully digital, no analog, 4 bits fit into one transistor. Hmm. In one clock cycle?