My guess is it's just another way of saying people like consuming media from companies that are relevant to their interests.
I personally find Snap's advertising to be nice. It's nice to have it separate from what my friends upload like what others have said. I've also found that what Snap puts out is way more enjoyable to look at than Facebook's advertisements.
Take sports for example. I'm a huge NFL, NBA, and MLB fan. Facebook's sports-oriented ads are usually limited to the game score which I don't need to look at because the game is already on my TV. Snap, on the other hand, puts up a nice collection of Snapchat videos from other people. I can get a pre-game locker room video from the players and I can get a fan's view of the game-winning touchdown in the same collection. Both are things you wouldn't see on a typical game broadcast. I'm fully aware that both are advertisements, but one is significantly more relevant and more enjoyable for me to consume than the other.
Lifestyle brands are a type of business as varied as Wired Magazine to Rayban Sunglasses. They aren't selling a product, but a "lifestyle" or a feeling. Some people legitimately feel differently when drinking Pepsi verses Coca-Cola.
If you see a popular guy wearing Gucci it can increase the value you give that brand. Gucci has a markup because of this "lifestyle" effect.
Edit: Lifestyle brand literally has a Wikipedia article on it, if you want to know more.
I like weight lifting as a sport. I once saw a video from a popular fitness band that had a ton of advice on proper form and approach before a competition.
I got a lot of value from that and would happily give my time and money to a brand that does the same for other things I enjoy
Telling "Apple" that you despise them for batterygate. Or tell them how much you really like the new touchbar. Stuff like that is "engage" with "brands."
I'm not a Snap user, so I'm not really sure what I would do. Send them a snap of my middle finger?
I'm definitely not anyones target demographic, but I do find some satisfaction engaging with Totino's Pizza Rolls.