Do a Google search for Sharm el-Sheikh airport and security and you’ll get pages and pages of experiences with corrupt and incompetent security.
Very easy to have a package placed in the baggage compartment. Very tempting with a planeload of 100’s of Russians and a A321-200 jet with the extra fuel tanks in the rear of the aircraft to toss that package in the rear baggage compartment for Admiral Ackbar.
That was my theory also but why would Russia want to dampen the bomb theory?
I heard that they have grounded their fleet of A321s but can’t find a web source yet.
We’ll find out the truth at some point but right now everything is speculation.