Yeah, that's not the app tracking XMR transactions, that's the app deliberately sending a note to relays to show them publicly. You can decide when you send xmr with garnet whether you want it to do this. You can send them private too if you want, which would just be sending an XMR transaction and no note to a relay.
I send them private sometimes, but I like to publicize them most of the time because it helps people see that XMR tips are actually flowing around and gets people excited and encourages everyone to do it also.