No. It is using a central “well known server” and requires internet.

Test:

    * Does it work in an airplane?
    * Does it work in a submarine?
    * Does it work in the mountains, when a thunderstorm is approach and you need to share the GPX?

Implementation shall be able to negoiate a connection locally (e.g. Bluetooth) and upgrade to peer-to-peer WiFi if need (Garmin doesn’t need that part, GPX are usually smaller than 1024 KB).

Modifications can be made to do that minimal peer exchange over BT. They may already exist, but I haven't used that part yet.

It seems like a lot of extra work to reinvent the wheel and get the security wrong instead of extending a well established protocol with many other tools built on top of it.