By the end the interviewer was telling it was all right for me to have mistakenly thought the registers were 32-bit words, and thus concluded the machine wasn't

By the end the interviewer was telling it was all right for me to have mistakenly thought the registers were 32-bit words, and thus concluded the machine wasn't quite Turing-complete, and he was noting that our analysis should still work for the Turing-complete version with bignum registers.