But block mode terminals that did forms had been a thing for over a decade at that point. Not that this was likely at Apple. But there are definitely contemporary ways in which one could have been entering this stuff via a computer.
Indeed, an IBM 3270 could be told that a field was numeric. This wouldn't have the terminal prevent negative numbers. The host would have to have done that upon ENTER. But the idea of unsigned numbers in form data had been around in (say) COBOL PIC strings since the 1960s.
* https://ibm.com/docs/en/cics-ts/5.6.0?topic=terminals-3270-f...
> Bill Atkinson, the author of Quickdraw and the main user interface designer, who was by far the most important Lisa implementer...
> I'm not sure how the managers reacted to that, but I do know that after a couple more weeks, they stopped asking Bill to fill out the form, and he gladly complied.
Notice that it doesn't say "they stopped using the form" but "they stopped asking Bill to fill out the form". The rules are different at the top, they probably still used it to mis-manage junior employees who didn't have as much influence.