There is back end (server side; PHP, or an Xojo app) and front end (in web HTML+CSS+JS). Xojo does a front end code that works in sync with the back end code exchanging “messages” all the time. So when you click a button in Xojo to make a sum of 2 fields and present a result, a JS code reads such values and send to the Xojo server that execute such sum there and send the result back and a JS code will present it. When you write both codes with separation of concerns in PHP+JS, you notice that for such task you don’t need to send anything to the server, you can solve everything in the front end code, so you get the values, sum them and present the result without sending anything to the server. Instantaneously. Many other things too you can design trying to squeeze bits of extra speed and only talk to the server when you really want something there (like reading/writing to a DB) but all the UI parts works detached from the server using JS to run them. Your friend probably is taking advantage of JS codes more than PHP codes to pass such impression of snappier code.