Go ahead and believe it was an airplane if it makes you feel better. My lighting expert makes a living at what he does. You are an amateur.
Amateur at what, exactly? Radar operations and maintenance (auto-track/surveillance)? Nope. Amateur at knowing what the different targets (missile or aircraft) I track are? Nope. I do this for a living, and have reached the highest level without having to go the engineer route. I have watched events like this real-time for years through a lense system that runs 6 figures, not including the camera itself. I can see the ISS through the boresight camera when we track it, this system is so good.
It was way to slow to be a missile, and moved at a constant speed. Missiles reach maximum velocity very quickly after launch. It would not be in sight very long. Ballistic missiles tend to run at around 9k mph, and reach that speed in short order.
In the end, it begs the question “Why am I arguing with you?” You believe it was a missile launched from a sub a mere 35 miles off our shores without us knowing that a boomer submarine was there. Believe it if you want. No skin off my nose.
Have a pleasant day.