I like this theory and the reasoning behind It, and I have a few things to add as well, If you have not seen these already...
in the prelude Kalak notices that the red, orange, and purple blood mix. We know from chapter 13 that the blood from chasmfiends is purple, so it is not so much of a strectch to say that chasmfiends could have been there.
Brandon also said to someone who asked "What are the smoke-y spren that appear around a dead chasmfiend?"
"They are in a symbiotic relationship with the chasmfiend, and are part of what allow the creatures to grow to the size they do with an exoskeleton. (Along with a high-oxygen, lower-gravity world.)"
The chasmfiend could protect the spren, and in return the spren help it grow larger.