The article, if examined by a non-specialist like me, seems to contain an answer to this concern at the end:

> There are papers that claim to have factored 21 with a quantum computer. For example, here’s one from 2021 [1]. But, as far as I know, all such experiments are guilty of using optimizations that imply the code generating the circuit had access to information equivalent to knowing the factors.

[1] https://arxiv.org/abs/2103.13855