You're probably right about that thought process. I see no harm in people giving credit or providing a link to where they got the meme from, if they know it.
Something easy that people can do if people see their meme reposted is put the link to their meme as a comment on it, with an explanation of what happened. That way people can see both memes, if they want.
But please keep in mind that in most cases (at least that I've seen), when people complain about a repost, it's not because it's their own meme. Often they don't provide backup, and just make an accusation based on their impression they've seen something similar before. These could be completely unintentional - just a person making a similar meme as someone else without knowing (so an accusation of reposting is unkind and inappropriate). Other times, the complaint comes because it's a meme that has been reposted frequently and has been seen numerous times. In those cases, it's hard to know which one is the original.