It sounds like you have tailscale setup in the container with userspace networking — which works smoothly for incoming traffic, but for outgoing traffic to use the container’s tailscale device it has to be routed through a proxy that tailscaled runs, otherwise it goes over the host’s network.

I haven’t tried with orbstack, but it is possible to setup containers to use tailscale with kernel networking by mounting /dev/net/tun into the container. With that setup outgoing traffic will automatically route to the tailnet as the container’s device (and you don’t need tailscale on the host at all).