In this instance I'm with you.
You'd already identified a desire for garden furniture, done your research and now the one you want is on offer - snap it up. This is a considered purchase, not an impulse buy, so it is a genuine saving. It's also at the right time of year for maximum summer enjoyment.
Is it that he doesn't want garden furniture, or doesn't like this set?
I would consult DP from a taste perspective and would have mentioned in advance my desire for the furniture, so would already have tacit agreement there (more just checking in my case but that depends who cares about how things look in your house).
I'd see the meal out as 'throw away' money compared to the furniture, especially if it's a casual 'because we want to' one, not a planned meeting-up or occasion.
It does read a bit as if, as the high earner, he has discretion over treats - so it's up to him if you both eat out or not. Would you be as free to propose that?
I'm not really sure why that would relate to household items. To me that's a separate budget. But if both are just 'discretionary spending' and do actually affect each other (can't you do both?), then my vote would be for marking the start of summer in your own garden.