They sure do. InvokeAI is a fork of the original repo CompVis/stable-diffusion and thus shares its fork counter. Those 4.1k forks are coming from CompVis/stable-diffusion, not InvokeAI.
Meanwhile AUTOMATIC1111/stable-diffusion-webui is not a fork itself, and has 511 forks.
https://github.com/invoke-ai/InvokeAI