He used the technology tag, which is picked up by the tribe. Steem Engine 101 indeed.

For onlookers:

(The reason why a 1% downvote is needed is because that's the only way to remove STEM rewards or hide unrelated content. The tribe accounts have little SP to prevent damaging target's STEEM rewards. That's a limitation of the system. It's not always wise to outright mute/ban an account from earning those tokens altogether. But in his case, the tribe opted for that route after reading all these bs.)