A fan over on Discord ran an estimated timeline of Melody, DMD and SL combined and estimated this scene takes place roughly 1 year after Ashley and Sis move away from Gerald and MC.
This would mean that either Gerald left the navy by this time, or he was doing what, in the US military, is called “off duty employment”. Personally I like the, later explanation as it gives the Gerald story thread more flexibility.
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I am not saying the above fan timeline is canon, but it is certainly close imo.