If you Google thrust washer Honda you will see a lot of threads with various sizes of engine. Honda have attempted to fix the issue on some engines but not the 150 in question here for whatever reason. Or, I can't find a service bulletin for the 150 I should perhaps say
I think the OP has been unlucky with it failing. Others have had this issue even with a solid service history and in warranty so who knows if it could have been prevented. I agree that sitting idol is probably not a good thing but others reported failures in heavy use so perhaps it wouldn't matter.....we'll never know.
With that said, I still expect Honda to say beat it and OP is out whatever for a new motor and you can't really blame them unfortunately.
Unfortunately, you will find design, or perhaps tollerance flaws is a better term?, with everything if you look hard enough. my own zuke 200 v6 (150 upwards I think actually) has been known to digest butterfly screws and writing it off for example. Thankfully threads like this are there and forewarned is forearmed and I have the chance to keep an eye on it (5 min job for mine).
If anything good comes from this it is likely to be how someone can check for this and if it can be fixed/prevented to help future owners of Honda's, at the very least others can go on THT and perhaps find out how to anyway. There are simply too many Honda's about to be bad motors so this is probably a rare thing to happen thankfully, my neck of the woods has loads of them anyway.
If I owned a Honda under warranty I would ask this also be checked at service time just to be safe.
P.s the F1 Honda engine is abysmal ATM. F1 engines are not pushed to the edge anymore sadly. Also merc e.g aint had a dnf due to engine this year so it is possible, one for another day on another subject though.