"It was a male primary school teacher that led a session at school for parents/carers on different learning styles etc. that told us that the muscular development of boys made fine motor skills more difficult at an early age (or something close to this, I can't remember exactly, 'twas last year)"
Really? All boys have more difficulty with fine motor skills than all girls? For most traits for which there are observable statistical differences between the sexes the difference is very slight (something like "the average girl is more [whatever] than two-thirds of boys" -- which still leaves one-third of boys who out-score half the girls in whatever trait is being measured).
So making generalisations like "boys have poorer fine motor skills" or "boys have a greater need for physical activity" is unhelpful and largely irrelevant. Some children have poorer fine motor skills than others, and there are some strategies that should be employed to help with that. On a population level, statistically more of those children will be boys than will be girls, but not actually all that many more. And in any individual class the numbers could be equally split, or there could be more girls with poor fine motor skills than boys. Similarly, some children have a greater need for physical activity than others, and there are some strategies that should be employed to help with that. On a population level, statistically more of those children will be boys than will be girls, but not actually all that many more. And in any individual class the numbers could be equally split, or there could be more girls than boys with a need for regular physical activity.
If you get hung up on "boys are this, girls are that" theories in education then it's wrong and detrimental to both the boys and the girls who don't fit into those neat categories -- who may be the minority (although in any given class they could be the majority) but even so are likely to be a very sizeable minority. Thinking about the different needs of children as individuals and then mentally grouping those individuals into loose categories of "may benefit from such-and-such an approach"