I wonder if your example is a different kind of trade. When we trade time in a leisure situation, we're trading something more immediate and tangible. Whereas the transactional nature of the grandparent comment is more describing something more distanced.

An example of this that was told to me is imagine you're going to dinner with the in-laws (or maybe your best friend's parents). What would their reaction be if you took out your wallet and offered to pay them cash for the meal? As opposed to offering to e.g. bring a bottle of wine or helping to set the table?

Offering to pay might be the "transactional" trade meant by the grandparent. While offering to contribute [food | labour | goodwill] is more of the trading time in a leisure situation.

Typically, in accounting contexts, tangible is used to refer to physical products, such as mammoth meat, or stone axes.

Intangibles would be the gain or maintenance of reputation from going to have a meal at your in laws and all that jazz.

Regardless, in this context, trade is trade, one entity giving up something for another. Simply spending the time to go to your in laws for a meal is a trade. And while many would not cough up cash to show the transactional nature, far more would simply not go to the dinner (or go less often) and opt to spend their time elsewhere.

Or, if the in laws have something you want, maybe you opt to spend more time with them.

I am not claiming one has to solely view every interaction through this lens, or should. But it is a component of most every interaction. You could strike up a conversation with a stranger with no ulterior motive and then it carries on too long and you start thinking I could spend my time better elsewhere.