All batteries can develop a memory.
The theory is that a deep cycle battery is specifically designed to be almost fully drained in order to keep it's deep cycle memory. When using it as a starter battery (especially on a vehicle that starts up quickly like the X) it doesn't get fully drained before getting charged back up.
Reality of the situation is that normal batteries also don't get fully drained before charging either. So it's not really a big deal. And you can be satisfied with the knowledge that the battery will hold up better if you happen to leave the lights on overnight a couple of times. It won't hurt the battery.
Some deep cycle/starter batteries are also used in diesel engine applications where they end up cranking for a bit, or have a massive drain on the system to start up.
I wouldn't worry about it. You did good. Be happy with it, because your still ahead of a lot of folks here.