Lighthouse doesn’t give the “Serve images in next-gen formats” message just because they’re are pngs and jpgs on the page. They take those images, convert them to wepb, and then compare the file sizes. If the converted image results in a certain amount of data savings then it’ll give the message. Since HubSpot is doing the conversion on the server side the file size Lighthouse will see is that of the converted image so when they do their size comparison it’s not going to result in any savings thus yes, technically, Lighthouse “knows” about the conversion.