Why is the verb 変えれない instead of 変えられない

Question

the only two reasons I can think of are politeness(he is talking to himself) or because it might be confused with the passive(because it's potential)

Answer 1

This is called ら抜き言葉, 'words without ら', and while it is often used informally by younger speakers, it's non-standard and therefore can make you look sloppy if you use it in a formal environment. It can apply to any 一段 verb, so long as you can use the potential with it: いれる, 見れる, 変えれる, 食べれる etc. Note that when an 一段 ～られる is passive rather than potential you cannot remove ら.

It most likely arose because, for 五段 verbs ending in ～る, 「～れる」 is the standard potential form, plus it creates a distinction between the passive and potential forms.