Maybe they wanted to demonstrate why bolted flanges are used on high pressure tanks and pipelines (when welding can’t be done). If so they were successful.
What kind of ‘glue’ will withstand 5000psi of pressure, repeatedly?........................
“bolted flanges”
I imagine bolted flanges use o-rings for sealing. Their seal becomes tighter as pressure increases and there is no glue involved. And the gap between the bolted flanges would be in the thousandths of an inch. That o-ring isn’t going to squirt through.
I can’t imagine glue being used to connect any parts of that submersible that were subject to the high pressures.
Perhaps glue was used as a seal for, say an electric wire going from inside to outside of the craft. Epoxies harden to quite a solid plastic.
I noted the flanged connection(flat) but did not see the gasket. In high pressure service, I would at least expect to see a metal ring joint connection.