Source for the malware claim?
> Programs are also considered malware if they secretly act against the interests of the computer user.
There are two criteria that software must meet to fit this definition:
1. The software must act against the interests of the computer user.
2. This must be done "secretly".
I unfortunately do not know much about the Reddit App for iOS so I can't make a judgement as to whether it fits definition 2. I think I can say with confidence it fits definition 1.
Maybe I am wrong.
I guess a non-malicious way of collecting the data for ad purposes could be to collect it locally and offer the user to review it before sending it off.