Why are old questions (mid 2015 I.e.) re-appearing as "active" in the stackexchange app on Android, even if they have not been recently modified? Personally I think it doesn't make sense to "bump" them up by the system, since the half life of video, especially video-software questions, is really fast...
This is an automatic feature of the system. The community user occasionally bumps posts that it thinks could benefit from attention up in the system. You can read more details about the process here.
It is intended to encourage review of content that hasn't been touched. Users that look at it can either vote the question down if it is no longer relevant (which will prevent it from appearing once it goes negative) or can vote up a useful answer to acknowledge that there is a worthy solution (which will also prevent it from coming up again.)
Sometimes this works better than others, but overall it isn't that bad of a process because it is easy enough to make the necessary changes to prevent them from coming up again, it just helps prevent stale data by bringing things up that need to be worked on in one way or another, whether to reduce the relevance of the question, to acknowledge the relevance of an answer, or to find an answer for a relevant question that is yet to be answered.