There is no fixed rules about the words.That's right. It just looks a bit strange.maybe a type mistake.

yeah, logically we should use 乙

Mostly, we use '甲' and '乙'. It is still odd to me. Since it's a joke. I guess maybe 乙 has already laughed to death by 甲's joke and he can't even murmur a word.

because it's a dialogue... 甲=A，乙=B... A (says) “今天 在 网上 看了 一下车， 发现 没一款车 适合 我 的。” B (says) “你 想要 什么样的 车？” A (says again, replies the question) 微信 红包 抢的 钱 就 能买起的…”

If this is a “two people talk”,you can use “甲” and “乙”，“甲”and “丙”，or “乙”and“丙” on behalf of the two people.If this is a "three people talk",as you see,maybe the "乙" will join the talk. ：）