Preface: It took me years (decades?) to realize that what happens in each person's brain when they 'think' or 'remember' is very different.

I often have perfectly clear memories that don't fit into any cohesive story. I reject them under the assumption that they're a dream leaking into my waking subconscious, or neurons going crazy, or whatever. (If this were a sci-fi movie, they might be critical foreshadowing!)

I wouldn't describe memories as inherently chronological. They're an unordered heap, with various indexes. Time is one such index, but a weak and incomplete one. I often misremember the age (or relative age) of events. Location and mood are much stronger indexes.

I haven't had any memories of being a Martian, true, but given that there seems to be some automatic filter already (most dreams don't become memories), it doesn't sound unreasonable that my brain has a GC of sorts. Perhaps my filter threshold is set too low, but still high enough to reject the Martian memories.

I agree that Boltzmann Brains are not the most likely explanation, but reflecting on how my memory works doesn't seem to be a good argument against that scenario.