Does Comcast cache websites thru public IP Address as a way to “boost” speeds?

One of my customers recently updated their main website. I visited the site from my office and got the new, updated site (the office is not on Comcast). I later went to the same site from my home WiFi using the same browser and the old site came up. I switched to incognito mode and still got the old site from my home computer. Back at the office today, and the new site comes up.

Seems kind of shady if Comcast promises "the fastest internet and download speeds" when in reality, they're not really connecting to the latest version of a site--am I misunderstanding what is happening here?