Heliophysicst here. This is not true. The flare that hit Earth on December 14th was an X-2.6 flare. While this is a large flare and the largest of the current solar maximum, it is nowhere near the largest ever recorded. The largest was on November 4th, 2003 (referred to as part of the Halloween storms), which was so strong it actually saturated the detectors. It was measured at an X-28, which is more than two orders of magnitude larger than Thursdays, but was estimated to be much larger than that.