No, definitely not true, Moehat. This was a pedigree British Blue heifer calving in to a pedigree British Blue sire - her first calf, calved with assistance. Wouldnt use a Dexter if you paid me to - nasty bad tempered little feckers!
Charollais are usually fairly good natured - flighty rather than anything else - but they can be bloody enormous and appear more frightening than they probably are.
However, NO ONE should ever walk through a field with newly calved cows, especially if you have a dog with you. Always either go around or turn back, even if there's a footpath through the field. 98% of the time, the cows will be fine but it's the other 2% that's the problem and nothing is worse than a protective cow, not even an agressive bull. She will kill.