If they did that it would be pretty easy to spot for anyone looking, all the bot accounts would be connecting through the same IP address(es). For it to be believable, you would need thousands of Ukrainian IP addresses, owned by Ukrainian internet providers. What Russia did is an effective way to achieve this. With thousands of sim cards on multiple Ukrainian mobile networks, the traffic is very hard to distinguish from real Ukrainian internet traffic. Of course the downside is that all the devices with those sim cards have to be in Ukraine for it to work. It’s also possible that at least some of these devices were essentially just acting as VPNs for more devices in Russia.