I think people are being a little unreasonable with what they expect from communications in situations like these. The employees dealing with this are focused on 2 things:
1. Resolving the issue
2. Communicating scheduling impacts to customers
The person in charge of posting alerts probably heard from dispatch that there was an issue in the USRC and it was effecting all trains. This was likely before they had confirmation of the derailment or a disabled train. The priority is get an alert out, and getting details isn't that important to customers, so saying a signalling issue is fine on first release as they likely don't have confirmation of the base issue.
They soon updated that to a disabled train, which is correct and less alarmist than saying derailment. They may not have even known it was a derailment as that detail isn't important to the message. Announcing a derailment will likely lead to people assuming something much more serious (think train on its side, or a collision), which isn't really a good communication strategy
Scheduling impacts and shuttles are likely being arranged on the fly and constantly changing as the situation evolves, so relying on local station staff and CSAs to communicate will allow more accurate information transfer than trying to get every detail in the online post.