A possible explanation is that the sender's machine is infected with some malware. When you receive an email from Bob, by definition, Bob's computer saw the whole contents; and also your email address. It seems easy, for some malware residing on Bob's computer, to send some spam with the same word, on the basis that you may be interested in the subject.
It is one of the dark points of spam: you get spammed because the machines and address books of other people are plundered by malware.
Another possible explanation is coincidence. You received an email with "Raspberry" in the body. But think of the millions of people who may also have received spams with "raspberry" in them while that had not used that word previously; and of the other millions of people who did send emails with "raspberry" in it, and yet did not receive spam containing that word. None of them posted in security.SE. Technical term is the anthropic principle: if you bring your attention only to seemingly "extraordinary" situations then you will see at lot of them, but not because they happen more often than predicted, only because you choose (more or less consciously) to disregard more "normal" occurrences.
My server keeps a copy of the last two weeks of spams that I receive and that my antispam filter automatically recognizes. That's, right now, 1170 spams (a figure which is not very big; around 2008 I was receiving more than 400 spams per day). Among these 1170 spams, one of them happens to use the "raspberry" word (as part of an email address), and that's not for my own using that word.