Well, from the user who shared his bonus offer from stake.com I don't think he said anything about him being inactive
It's just a speculation.
None of us, claiming is a correct or 100% true. But, inactive account could be triggered the bonus. My friend who active on slots and suddenly not playing on Stake anymore due playing on other casino.
Got offer triggered for 25$ bonus with waggering too, in stake you can't expect a correct answer. All the things we shared is just based speculation or 2 cent from us... but is worth to tried.
It does not worth to try if we are trying to be inactive merely in a hope to receive the bonus because there is no guarantee. I mean, it is better to be inactive because we want it or because we should do it for other better reason. If we become inactive in a hope to get the bonus, we may get disappointed later once we are inactive for a while but there is no bonus offered by Stake.