Ecowitt Wittboy - no values without internet?

I have recently purchased an Ecotwitt Wittboy to solve some local weather information stuff (mainly wind sensor for use in automations).

While I am more or less satisfied with the product as a whole, I tried to eliminate any communication of the device outside of my local network.

Therefore, I have put the gateway on a VLAN group including my HA server but not my internet router.
However, I found, that after a while the connection between the Wittboy and HA has been lost and no sensor values had been transmitted any longer.

Once I include the internet router in the VLAN, the transmissions seems to be constant.

As a plan b, I tried to block URLs contacted by the Wittboy with Pi-hole.
It seems as if the Wittboy mainly contacts an OTA firmware server from ecowitt and a ntp server, which should be fine i guess.

But, there is still one thing I am worried about:
In the local network section of the webui, a static DNS server is set to 205.171.3.65.
I did try to change it, but it always reverts itself to that address.

I was hoping to use the Ecowitt Wittboy as a mere offline sensor submitting to HA. These seemst to be not possible though.
Do you have an ideas how to achieve that?

I can tell you from reading the manual and looking at the communication on my network. the manual says ecowitt.net will host all sensor data.

The Gateway is literally just a Gateway. It connects your sensors to your wifi then to ecowitt then to the APP and your Custom Server. So the DATA goes out then comes back to the local server on HA.

I don’t know if the data is encrypted, but if not, you can get a 915 MHz receiver and build your own gateway.

Thanks for that insight.
I was under the impression that Ecowitt works completely offline hence the integration is classified as local push: Ecowitt - Home Assistant

@D101 , I spoke with Ecowitt support, they say it is possible to get the sensor data without connecting to their cloud server. I told them I was not able to, they are looking into it.

Thanks for the effort mate. I am curious of the outcome…

Still I feel a bit confused and unhappy because the Home Assistant integration classification is suggestion truely local connection which it is not the reality right now.