Not knowing the exact URL for their web portal (which I'm pretty sure isn't public but only a stopgap within their own WiFi network), I checked bugmenot for walmart.com.

I got this error...

walmart.com logins

This site has been barred from the bugmenot system.

Sites should only appear blocked here if they match one or more of the following criteria:

Pay-per-view: users pay money to access the site
Community: users register only to add/change content (but not to view)
Fraud risk: user accounts contain sensitive details e.g. banks, online stores, etc

I'm not sure what their web portal page URL was or I'd check and add it. Either way, anyone can pull the same trick themselves using any random username@dispostable.com

I'm not at Walmart right now to check their web portal page, and my current internet connection is apparently being slow as molasses, but I'm saving your comment to check later..