Actually February 1779 was hotter with a mean of 7.9:
But if you think that a mean temperature is any indication of reality you really do not understand statistics. A mean is not an actual measurement it is a statistic calculated from a series of measurements. So if you are comparing mean temperatures you must include the standard deviation for it to be of any relevance. Furthermore, the raw mean values mean nothing if all the other confounders of the data are not known or taken into account such as urbanisation. The urban heat island effect adds at least 2 degrees to modern urban temperatures and very recent papers have shown up to 8 degrees. A recent freedom of information request to the UK met office showed 29.2% Met Office sites are rated by the World Meteorological Organisation (WMO) as CIMO Class 5, and this comes with a warning of “estimated uncertainties added by siting of 5C°”. Class 5 can be termed a ‘junk’ rating since the WMO gives no guidance on where it can be located. The next to junk Class 4 comes with uncertainties of 2C°, while Class 3 has a 1C° warning. From information disclosed under a Freedom of Information request Class 4 accounted for 48.7% of the Met Office’s 380 recording stations. Only 13.7%, or 52 stations are free of ‘uncertainties’ warnings.