Please help me understand this strange echo-HA relation

I am completely confused with what is happening. So, can somebody please explain it to me.

I am running HA on my RPI4 with no cloud subscription with just a few esphome and zigbee2mqtt stuff.
I have added 2 shelly1 switches, flashed with the esphome to the each of my active speakers to turn them on/off when music is playing. That works as expected.
I have created group so both speakers turn on together.

Recently I bought amazon echo on a big discount recently and installed Alexa media Player addon HACS to play with it. I used to hate the idea as I prefere it all local, but it is kinda fun, and I ended liking it for some things.
Alexa discovered one an only HUE light, but also my HA “Speakers” group and I am able to turn it on/off by the voice command. As I don`t have any cloud subscription I find that rather strange. No other esphome stuff is found, as expected, but maybe it somehow sees just the groups. I have created group.lights and added few entities, restarter HA but no. Alexa sees just group Speakers. Than I have added another entity to the group.speakers, restarted HA and I was able to turn on/off all thee entities with the voice command.

So, big question is how come alexa sees the HA group.speakers, and why does it not see other groups?