On a scale of usual to extreme thats probably about right. Though averages for, say, Pamplona, Leon and O'Cebreiro may vary from that norm by a fair amount. (Subject to the number of Pilgs per cubic metre of occupiable space and whether the "open windows" or "closed windows" adherents are in the effective majority)
You might want to look at averages and extremes for various key points along the Frances rather than an overall average. Bear in mind that, at Samos for example, the external temperature has no impact on the internal temperature which has been as cold and damp as the grave for well over a thousand years. Whereas at Serbal y la Luna in Pieros there will be so many, densely packed, pilgrims digesting a three course garlic feast that the internal temperature will reach tropical heights.
Take a two season bag and you'll be comfortable most of the time.