i seriously doubt the user they said is using multiple phones is legitimately running around with 30+ phones on himself to mine mcz
your comparison is also invalid because this is not the same as traditional mining
the objective here is to promote users to gain an incentive whilst being active in a positive manner, not promoting them to get their hands on as many devices as possible just to sit back and make bank
Yes and how you can imagine, preventing people from owning multiple phone?

There is literally no way to prevent people from installing application on multiple phones,
maybe except from requesting passport or some kind of identity authentication, which
would be just ridiculous! As for cryptocurrency.

P.S.
youcantbesrs:
that can easily be modified to do just that
albeit it is just a rough example that i threw together in 5 minutes
without access to any of the backend information the devs themselves have access to
yes that is the thing i was talking about, it can be made pretty easily.