I would not give money - you would either be offering peanuts for valuable tups, or too much for older animals. If he wanted to accept money then he would have at the original point. Farmers are business people and don't do the 'oh no I couldn't possibly accept anything' approach, while meaning 'gimme', then accept once you insist. It isn't like that.
He is getting free grazing, with somewhere to keep his tups well away from his ewes.
He should indeed have walked the pasture before he put them on there. As you say, you are not smallholders so he should not have assumed that you knew enough about livestock to be able to protect his animals - it is his responsibility.
There's no such thing as a free lunch, as he now knows.
You have apologised and learnt from your mistake, he has accepted your apology. Don't grovel.
Find somewhere else to keep your grass - in fact make a proper compost heap and preserve your fertility, instead of chucking it away.
For me, this tale demonstrates why you should always have a formalised agreement when letting out land, even with no rent charged. Both parties know where their rights and responsibilities lie.