Honestly, I wouldn’t find that in any way problematic in itself. Memoirs are selective and will routinely rearrange timescales for dramatic effect, to remove extraneous events, leave out people who don’t want to be in your book, or because an editor has said ‘This interrupts the flow’. And people in real life do completely illogical things that you’d look askance at in a fictional character, like going to be taught to surf by your adult child while you’re about to have your home repossessed.
The TSP is an extreme example, obviously, which is why it’s causing so much speculation and outrage, but if we leave out for a minute the embezzlement and the problematics of the timeline and severity of Moth’s diagnosis, I don’t think that there’s anything particularly unusual in a memoir in omitting a visit to their son, who may have asked not to be included — he seems to only feature in TSP in a single conversation, in my memory?
Quite apart from the specifics of this case, I think people are being quite naive about the extent to which any memoir is a literal ‘warts-and-all’ slice of life.