They had no idea... that's why they checked. YOU knew it was a cake.. they didn't....
I understand many innocent things show up on the screen looking very much like some... well... very UN-innocent things!
Last trip I had a trophy plaque from a shoot in Utah in my carry on.... made form ROCK...that got their attention too... I think it is a density thing when scanned....
Is Red Velvet cake particularly rich/"heavy"? Sorry.. I don't know what it is... (but it SOUNDS great!^)
EDIT: I just googled it and saw some pictures...... MMMMmmmmmmmmmmmmmmmmmmmm!!!!!!!!!