There's nothing about this at the Mt Washington web site, but I joined and posted to their forum:
Title: WMO lists new wind gust record 113.2 m/s (253 mph; 220 kt)
I know of some event that challenged the MWO record, but I'm not sure if this is the same event or not, I think not. It is from 1996, I'm not sure what took them so long to investigate, this sounds like a new declaration.
The folks at Mt. Washington view their record with great reverence, I'm surprised the site is silent about it.