What could cause the glitch? Bad data. That can happen at any point from the acquisition to presentation phases of the data's lifecycle. FA could put some data cleansing/range validation logic in place, but it's obvious/innocuous enough that the don't bother, apparently. Errors also occur when data is "Flight Aware" sourced - estimated, ADS-B, etc - i.e., not real ATC data.

(or perhaps it's not obvious - I remember a thread where someone was worried that a flight dropped 4,000 feet in a minute and climbed back to the original level a minute later, all in the cruise phase of flight. They though the turbulence must have been really severe)

EDIT: I just noticed this flight reported an 11,000 ft/min climb. Impressive, from a 738.