Literally said so in the article: "...., build loyal affiliate partnerships."
Looked at the content and it's perfect for making money.
First there's reviews of a bunch of coffee gear,etc so people find the site googling for information about said coffee gear.
Now once on the site there's ads for other coffee related items from these affiliates with a reader who's already thinking about buying coffee related items so the so called "conversion rate" is probably very high (meaning that the ratio of people visiting the site who both click an ad and actually buy items is very high (Yes, there's different rates depending on the customer actions but assume they pay relatively well)).
The blog was making $30k profit and got acquired for $1m? Doesn't that seem super low? Obviously this type of exit wouldn't have VC-startup multiples, but still.