Is walking off the job quitting?
In terms of whether walking off the job without comment could constitute quitting, a lot depends on the specific circumstances. For example, it would be different for an employee paid on a salary basis, where the exact hours worked are by definition not critical, as opposed to an hourly worker, where the worker is expected to be there for a defined shift.
The nature of the job matters, since there are some jobs where leaving constitutes a direct failure to do the job, such as toll or ticket collectors, receptionists, nurses, and security guards; versus jobs where continuous attendance is not necessary, such as many office jobs. It also matters what, if anything, was said before walking out and what prompted the employee to walk out.
So, there is no single answer to the above, though clearly there are many circumstances under which walking out could be taken as a resignation or quitting. However, more to the point, it does not really matter. Even if walking off the job were not the equivalent of quitting, an employer (at least in the absence of an employment contract to the contrary) would be justified in firing the employee for cause (e.g. insubordination; violating workplace policy or terms and conditions of employment.) Being fired for cause has the same legal effect for most purposes, such as eligibility for unemployment insurance, as resigning or quitting.
Just as many employers would consider an employee’s walking off the job to be quitting, and it would be difficult for an employee to prove otherwise or take action against the employer for doing this, many other employers would choose to fire the employee for cause for walking off the job. In either event, the worker would be ineligible for unemployment compensation.
The key factor is that the doctrine of employment at will—which holds whenever there is no employment (including union) contract—gives employers enormous latitude to terminate employment. Essentially, there is no right to a job, so if an employer wants an employee gone for walking off the job, the employer can get rid of that employer, whether it’s accepting the employee’s resignation or firing him or her. This is a case where the workplace culture, attitude of the employer, and the employee’s relationship with the employer and any supervisors matters more than the law.