The calculators were released in 1999 and 512-bit RSA was strong enough for that time period.
"Moody used two free implementations of the general number field sieve, msieve and ggnfs; the computation took 73 days on a 1.9 GHz dual-core processor. This demonstrates the progress of hardware development: the factorization of the similar 512-bit RSA-155 in 1999 using the same algorithm required a large dedicated research group, 8000 MIPS-years of computing time, and a Cray C916 supercomputer."[1]
I might be mistaken, but I believe sneak was referring to the general irony of using RSA, whose underlying strength relies on the math problem of large number prime factorization, as a deterrent to keep out calculator enthusiasts, who presumably would find such a problem interesting. (Rather than the suitability of the key length of 512-bit RSA, which as you pointed out, was good enough back then)
However, I guess the same could be said for RSA being used in any product used by technically-oriented folks.
"Moody used two free implementations of the general number field sieve, msieve and ggnfs; the computation took 73 days on a 1.9 GHz dual-core processor. This demonstrates the progress of hardware development: the factorization of the similar 512-bit RSA-155 in 1999 using the same algorithm required a large dedicated research group, 8000 MIPS-years of computing time, and a Cray C916 supercomputer."[1]
[1] https://en.wikipedia.org/wiki/Texas_Instruments_signing_key_...