Actually you could do this with a VCR, and rather simply too, we used to do it all the time 15-20 years ago. and I know Tivo has not been around this long.
You were not doing the same thing, you were watching a live program while the VCR recorded something else. The TiVo innovation was to permit viewing of a recorded program while recording another program. You could not do that even if you had 2 VCRs, because you could not start watching a program from the beginning while it was still recording and FF through the commercials. Now that I think about it, Replay patented that ability which TiVo also had. Replay took a lot of heat from the NAB over that back in the late 90's IIRC.