So can my cell phone....well, not out to 4 bit numbers.
I suspect your cell phone can do numbers taking considerably more than four bits to represent: four bit numbers range from 0 to 15. The article also doesn’t tell us to what precision the square roots were calculated (seeing that 0, 1, 4 and 9 are the only perfect squares representable by four bits, that might have been interesting to tell us).
I’m underwhelmed. Just like I’m underwhelmed by the quantum computer that can use Shor’s algorithm to factor 15.