Sibling comments have good points but in addition: there are a great many legitimate reasons to bring a phone to the inauguration and many fewer legitimate reasons to bring a Raspberry Pi. These guidelines aim to reduce risk, not remove it entirely.
I think someone or a group really motivated to cause harm will laugh at these rules.
Just an anecdote but I was screened several times in the airports (more after 9/11 because of... face) but never caught a pepper spray or other prohibited non obvious items carried accidentally.
>are a great many legitimate reasons to bring a phone to the inauguration and many fewer legitimate reasons to bring a Raspberry Pi
By that logic, I assume they've banned ski masks, skis, fake snow and pinecones. ;-)